The user bank by default should have copies of programs from other banks, so you should not lose any patches by overwriting instruments in this bank. There is only one user bank.

You could either save the user bank through a MIDI SysEX dump to an external sequencer, or, if you want to restore this bank later and have not saved it, you can go to the Alesis website and download the factory original settings in MIDI SysEX files.