If institutional biases flip, does either party change their positions?

[Skill and Chance]

The Senate is effectively impossible to change because of the language in Article 5 requiring unanimous consent of the states and the likelihood that the party that benefits most from Senate apportionment by state will have a SCOTUS majority to enforce it aggressively.

SCOTUS is the second hardest because both sides know that if they go there (either by ignoring them outright or adding seats), then the law means whatever the incumbent president wants it to mean from that day forward (barring a supermajority against them in congress).  Most everyone recognizes that we wouldn't be a free country very long if that happens.   

Regarding the EC, it's plausible that a SCOTUS majority appointed by a party that lost multiple times in recent memory while winning the PV eventually finds WTA by state EV allocation unconstitutional.  Also, in the specific case where one party wins the EC while losing the PV and then 4 years later the opposite party wins the EC while losing the PV, I think it's reasonable a constitutional amendment would be passed.

Gerrymandering in the state legislatures is easy to change in some states and very hard to change in others depending on state institutions, namely whether that state has initiatives and/or elected state courts. 

Gerrymandering in the House is by far the easiest one to change because in theory all you need is a normal federal law spelling out a different process for drawing districts in every state or switching to PR or statewide WTA.  There's a constitutional argument that the House could even do this on its own without needing agreement from the Senate or President.

[Skill and Chance]

I think enough Dems hate the EC that even if it advantaged them they’d be happy to go with a grand deal to abolish it if it came to it.

But in a PV/EC split that favours the Dems, I fear that the Republican solution will be to refuse to certify key states that they control on the state level…

And then SCOTUS compels them to certify by at least 7/2, so long as the state law set prior to the election provided for the electors to be chosen by popular vote.