I am suing a hotel for negligence (injury)but I just found out they are trying to sell the hotel asap..how will this effect my case?

The hotel should have insurance, and that does not really matter who purchases the building or who operates the hotel.  Since you say you are suing, I would hope that you would consult with your own lawyer on this, unless you are doing this pro-se..on your own.  Since there's a serious injury, if you do not or have not sought a review with an attorney, you should.  If you have a lawyer, follow up with him or her on this question.