Most people are treating this like Abraham Lincoln or Martin Luther King shooting, but it's not. These people were liked and generally seen as good.
This shooting is more akin to a Hitler shooting, which he had survived many, and was not liked. This is not a martyr situation and most are not going to change their feels for trump.
I'm sure the republican party would have another candidate immediately. There were a bunch of other candidates that ran a little bit earlier this year for this election, but got like zero news coverage and dropped out. I know because I looked them up a couple a weeks ago wondering why I never heard of others in passing.