The brand is irreparably tarnished. It’s negative public image is insurmountable baggage to expanding its voter base. Yeah, it’ll be tough going at first. But there are no viable alternatives.
About two thirds of the cooks in the restaurant are bad, but the management doesn't care. The easiest way to make the management care is to find out who is cooking before you go. Cruz, yes. Cornyn, no.
By far the best strategy is to primary losers like Cornyn and Rubio, but management will sabotage that at every opportunity. When they do, the correct response is just to let a democrat have the seat.
This is bad, but usually democrats run more conservative people in red states/districts and a democrat in a red state or district is far easier to get rid of than a RINO. Plus the republicans managed to hand power to the democrats in the senate anyway in a presidential election year with a popular president.
It is worth remembering that the republican party absolutely sabotaged themselves for the entire four years Trump was in office out of pure spite for him. So you aren't losing as much as you think when democrats take power. Also, the more people actually experience democrat rule, the more they know how dysfunctional it is.