I'm not entirely convinced Governor Baker would have necessarily appointed a Republican to a Warren vacancy. Granted, he probably wouldn't have appointed a Democrat...but I believe at the top of his appointment shortlist would have been Marylou Sudders, the Massachusetts Secretary of Health & Human Services in Baker's own cabinet -- and a self-identified Independent.

In that case, Baker would probably have placed the onus on Sudders to choose whether she would've caucused with the Democrats or the Republicans (whether Sudders would have run for special election to that seat in her own right, on the other hand, is a totally different question). Charlie Baker has no future in the national Republican leadership...he would have had nothing to gain by appointing a partisan Republican to replace Warren.