Of course you wouldn't depart with it.
But, once it has happened, you are stuck with it.
You haven't answered my question- If it isn't going to get any worse, why is it safer to land immediatley than to carry it to a convienient base?
You also can't dispatch with only one RAD ALT- would you land ASAP on some marginal wilderness strip if THAT happened in flight?
Once dispatched, the MEL does not apply, and it is up to us to make the best decision we can with the info available.