POTS is not life threatening, just life altering. You can read more about POTS in some of the articles here:
http://www.medhelp.org/health_pages/Neurological-Disorders/Further-Reading-on-Dysautonomia/show/696?cid=196
Please feel free to let us know any further questions you may have. Getting a diagnosis may be intimidating, but really it's just the first step to getting treatment and feeling better!
Everything I've heard from docs is that it is not. It is disabling to some extent or another... sometimes quite disabling. If severe enough, it seems like wild HR & BP swings could be a problem... and certainly if there is some underlying heart condition or whatever, it could be brought out by an autonomic troubles... but to my knowledge, POTS is considered non-fatal.
There could be other conditions such as MSA (multiple system atrophy) that might show up as POTSy stuff, but do have poorer prognosis over time. But in your case the post viral POTS thing is considered totally non-fatal. I think I read that recovery from the post-viral POTS is also more likely overall... some people do recover well after enough time. I certainly hope you are one of them!