I am certainly no expert but I haven't heard of prolapsed rectums in chins either.. so I doubt it is very common.
I wouldn't let it stop you from aquiring another chinchilla..

Chinchillas are more likely to get problems with their teeth (the name escapes me at this time) but if you did have one that was affected with that condition, that shouldn't stop you from getting chinchillas in the future.. you just may want to get the next one from a good breeder (if you got the sick one from a petstore for instance)..
I'm sorry for your loss Leigh..
