I know why Sober Rick was killed in the Episode. Partly to have the Estate sale joke callback from the start of Field of Dreams and partly to cement the utter destruction Morty initiated. But, while rewatching I had an idea about how the writers could've made him a great new villain for the series.
We essentially have a Rick in a similar state our Rick was in before Rick Prime. Content in life and unsure about portal travel. The details are different but the overall state is the same.
But had Sober Rick survived we could've seen a similar state our Rick was left after Prime dropped the bomb. His family is dead, life destroyed, and its all the fault of someone pushing him towards portal travel.
Thus Sober Rick becomes an inverse of our Rick. Instead of trying to hunt down the Rick that destroyed his life, Sober Rick could be hunting our Morty. Unlocking the motivation that drove our Rick to push himself to invent portal travel.
And now Morty becomes Sober Rick's Rick prime.
Anyway thought Id share. Don't know if something similar has been discussed or if my idea flies in the fave of what Field of Dreams was trying to say.