[mike22]

If it’s a reasonable company, they will be willing to move your start date upon (polite) request, justified by the delay. In my recent job change, there were a couple of things that moved the timelines (only a couple of weeks, not months like your case), and the recruiter adjusted my start date like it was SOP.

Re resigning: make sure you have some concrete evidence of passing all contingencies in the hiring process (even go so as to ask the recruiter if any steps remain). Only after that, give your notice.