There may be legal recourse but the legal system moves so slowly that in Internet time you are pretty much screwed. So in the beginning stages it may be a good idea to keep copies of all software, data, etc. close just in case one gets locked out of the servers.

I know of this one company that decided to move their servers out of a collocation facility. The collocation facility hated to lose a good customer so they just locked the company out, disconnected the servers and did not let the company get to them. But they helpfully offered to reconnect the servers if only the company would sign another long term contract. The litigation took many years, so the data on the servers was pretty much lost for all practical purposes.

So yeah ... keep backups and keep them where you can get to them if the s hits the fan.

Regarding the domain name ... I suppose one person needs to have control of that, no way around that. Well, it is possible to set up a trust where an impartial party (such as an attorney or a professional trustee) controls the domain name according to a previous agreement between the founders, but if you have to resort to this, there is probably not enough trust to do a startup.