As far as I know, as long as you maintain insurance without dropping it, you can't be denied for a pre-existing condition. We have switched insurance companies 3 times since my diagnosis, and I have had no problems.
I'm not sure where you live, but if you lose your job in the USA you can purchase cobra insurance to carry you over until you get coverage again. (I've never been on it, so don't quote me, but I think that's how it works.) It is very expensive though. $500/month, I have heard.
I hope you end up liking your job. Sometimes my husband hates his, but I tell him how important the insurance is to me. (His insurance is better than the one at my work.)