Can I replace a DSI HWH with something (anything) else?

There are serious advantages to DSI water heaters... but one problem which you seem to have (DSI Faults)

I had to replace the control board on mine.

But to answer your question.. YES. you can replace it There are basically 3 types of water heaters (or 4)

1: Propane only manual pilot light. these have to be manually lit and many folks have problems doing that. and they burn gas all the time (pilot. not much but some).

2: DSI.

3: Tankless (Also DSI however often a better quality).