Posts below compare the survival and longevity of monitors in the wild, vs. monitors in captivity. This topic goes in several directions at once, so let's pick just a couple of items that might interest people who keep monitors in captivity: lifespan, and effects of the pet trade.
Who lives longer? One answer is that it doesn't matter – any monitor that enters the pet trade is "dead" (removed) as far as the wild population goes. Ignoring that for now, can we sort out relative survivorship in the wild vs. in captivity?
There are many ways that monitors enter the pet trade. The majority are wild-caught, with a focus on juveniles of larger species and adults of small species. A few species (savannahs, Niles, waters) may be "farmed", but this usually involves retaining WC females until they lay – mom is a handbag long before her CH juveniles hatch, so the farming is simply a value-added exercise in exploitation. The number of CB and CBB monitors is increasing, mostly for Australian species that have not been legally exported except to zoos for over 25 years.
However you look at it, CBB monitors have far higher survivorship and longevity than do their wild counterparts, in the sense that the average individual hatchling lives longer. The picture is less clear for CH and WC animals, but it seems certain that the vast majority of trade animals die miserably within a few months; only a few live to maturity, and very few indeed reach 10 years or beyond. How many hatchling savs, Niles and waters were imported in 1994, and how many of those animals are alive today? Probably this value is considerably less than 1%.
What we need to know, however, is what percent of the wild monitors that hatched in 1994 are alive today out bush? There are few scientific studies that can answer this question directly, but there is another way to approach it. If a wild population is to remain stable, each female must produce, in her lifetime, no fewer than two young that survive to reproduce. Making the assumption that wild populations are stable, all we need to know is the total number of eggs laid by an "average" female in an "average" lifetime.
For example, if a female V. tristis matures at age 2, lays one clutch of 12 eggs each year thereafter, and dies at age 6, she has produced 60 eggs, only two of which need to become breeding adults. A female V. niloticus might mature at 2 and lay 30 eggs a year for 5 years, producing 150 chances to get two replacements. A female V. prasinus might lay 4 eggs a year and die at 6, leaving only 20 chances. These aren't unreasonable (and are generous estimates, if anything), but they sure are variable – 20 vs. 60 vs. 150 – so what's the deal?
Different species have different clutch sizes. The biggest determinant of variation in clutch size among species is female body size, but the next most important is "ecology". As a broad generalization, those species whose juveniles must live in very open habitats (where secure refuges are few) produce more eggs/clutch than do species of the same size whose juveniles have access to solid refuges (trees, rock outcrops, etc.). Thus, things like V. albigularis, V. niloticus or V. spenceri produce larger clutches than do V. panoptes, V. salvadorii or V. salvator, for example. Small arboreal species from dense habitats (for example, prasinus group monitors) have smaller clutches than arboreal species living in open habitats (for example, tristis group), and so on.
Like most animals, monitors have a concave, "type 1" survivorship curve, where per capita mortality rates fall off quickly with increasing age or size. In other words, hatchling monitors get hammered, while the survival prospects of adults get progressively better. (This contrasts with a convex, "type 3" pattern, shown [now] by humans, where mortality rates remain low from birth, and increase only in the upper age classes.)
From this, the answer to the question is "It depends". Even if we agree that the survival rates of imported hatchling monitors are miserable, they may not be dramatically worse than survival rates in nature for species that produce large clutches. These are "live fast, die young" species anyway. The picture changes for species that produce small clutches, partly because most WC imports are adults. These species typically live longer in the wild than in captivity, if the average WC adult is age 3 and would live 3 more years in the wild, but few imports (think V. beccarii or V. prasinus) live a year as captives.
Effects of the pet trade. It follows from the ideas above that the effects of trade in live monitors vary according to the reproductive potential of the species, and the ages of the animals that are exported. It is always more damaging to remove X adults than to take X hatchlings. What really hurts is to take them all, as happens with CH farmed orphans from the skin trade. By contrast, CB animals start out being almost neutral, and may even become positive – if you'd rather have a CB hatchling than a WC adult, that's 100% in the right direction.
There are of course many other aspects of the WC/CH trade, such as ethics (but poor people can't care) and habitat conservation (but poor people can't afford to think ahead); however, the sustainability of the trade has a lot to do with the population biology of each species, and the size/age of animals that are typically exported.
