The question explicitly stated that booting another os wasn't an option, so you are right in this case.

However, you should avoid being in that situation entirely, which is nowadays very feasible: all modern servers include remote management facilities, and all sensible virtual server providers give you some way or another to boot from a network image (and get a console session through VNC).

If your provider doesn't give you these options you should definitely switch providers. Not having this option means that you are always one mistake away from total doom (server won't boot -> you will never ever be able to access it again).