Will some R's see the writing on the wall, lose enthusiasm, and stay home?

The early voting by party is very good for Hillary. And Trump with his rigged talk is basically encouraging his supporters not to vote.

It's supposed to be complacency that keeps people home apparently.

Although to be serious there is really no data either way and if anything your version is probably more likely.

... that there will be a lot of stay-at-home Republicans in this election.

There are GOP voters who don't support Trump, but don't want to vote Dem or Third Party. So they'll just sit this one out.

There are also GOP voters who see the "Trump can't win" writing on the wall, and feel that their vote won't turn the tide - so why bother?

It's simple. Too many Americans see voting as a hassle - and they're not going to put themselves through that hassle for (a) a candidate they don't really support and/or (b) a candidate who they believe is unlikely to win whether they vote or not.

wash their hair. or that is what I've seen all my life. It will be the same this time too.