The red states, and the purple states that are controlled by Republicans, should do all they can to BAN mail-in balloting.
This will leave it in place in the the blue states.
Republican/traditional-minded voters -- even in the blue states -- should eschew mail-in ballots and vote IN PERSON whenever possible.
That's because:
States that do not certify their presidential electors 35 days post-election, may be denied the vote of those electors when the electoral college convenes. Something called "safe harbor", I think it's called (could be wrong).
That means that states with mail-in ballots may find themselves in an awful mess if they can't COUNT those ballots before day 35 (post election).
Thus, it's possible that in such states, they may have to "go with the votes that are counted" and simply ignore the uncounted surplus of mailed-in ballots, IF they wish to have their state represented in the electoral college.
That's why a "vote cast in person" could become much more "consequential" in such states than a "vote mailed in". Just as you have to go to war with the army you have, states will find they "have to go to the electoral college with the votes they've counted".
By the same token, the states that continue to go with "election day voting in person" (i.e., the red and purple states) will have their electors "ready to cast their votes" when the electoral college meets.
Whether the Supreme Court will back up the "35 day rule" if states CANNOT meet it, remains to be seen. We'll have to wait and see.