The gadget is giving you a clue where you are .. in amongst the rocks and other hard things.
(a) if the signal fails, you don't want to be there ... unless you can revert to another procedure (with all that that entails) would you not want to do the miss without delay (but with the caveat that one needs to follow the procedure splays for protection) ?
(b) if you are outside a tight tracking tolerance, then that didn't occur suddenly and the pilot should be aware of what was happening. Either get back into the crossed needles without delay or think about (a)