Unlike the 70s-80s GM turbos, Volvos water cooled turbos rarely ever fail UNLESS the owner fails to maintain the car (like rarely changes the oil).

I work on Volvos for a living and have yet to replace ONE FWD Volvos turbocharger due to it being siezed. I have replaced a couple several years ago on new early 850s (when they first came out in '94) because the dealers sales manager thought they were "too noisy" and didn't want to sell a new car sounding that loud. Although the replacement new turbo was then quieter, there really wasn't anything wrong with the original turbo.

As for the old 700 with the inop (probably siezed) turbo, I too highly advise getting that replaced ASAP because those cars barely move w/o a turbo due to its lower engine compression. If you are carefull, a good used turbo could probably be found if the car's not worth the cost of buying a reman unit (not cheap).