I agree with Ralph. I have a 31 year old mechanical pump that was on my sons boat last week working. It was a fill in till his new one came in from Summit.
I would doubt you'll find any electic pumps that last near that long.

Definately use a block off plate and pull the old pump if you do switch over. No sense wasting HP
running a pump you aren't using.
Then again, you could let the pump on and have some spare hose for the day the electric pump quits.