Things will continue to slowly decline as the Baby Boomers die off and the realty of them clinging on to their jobs until their deathbeds sinks in; There is not going to be enough competent people to replace them in places like the federal bureaucracy and intelligence agencies.
You are right about Pence, which is exactly why I see them picking him then proceding to lose 2024.I don't think we're going to see Pence run in 2024. He's an empty suit who hasn't been very active in the direct affairs of the Trump Administration and has done so deliberately.
Pence is a relic of the Religious Right and that's too toxic of a platform for the Republican Party to run on the federal level. While Pence himself is fairly mild-mannered overall, he's not the kind of guy you'd pick as a major candidate for the 2024 Election.
Ted Cruz had a similar problem, but he's gone a long way to distance himself from his fundie past since 2018. Now Cruz has been building a newer and more positive reputation among the Trump base by going after Google after the Veritas leaks and he's also proposed major federal crackdowns against Antifa gangs, which helps his chances in a 2024 GOP run.
As for the Democrats, if they lose 2020, then I expect to see major restructuring. The Squad is going to be thrown under the bus if Trump wins in 2020. Whether that's done via having other Democrats primary them out of office or simply just sidelining them out of any real influence in Congress is anyone's guess.
A second term of Trump will be the much needed wake-up call for the Democratic Party because right now they are of the belief that 2016 was an aberrant fluke and are tripling down on all the things that cost them that election. A loss for them in 2020 is going to send a message that going woke was a mistake.
Assuming Trump wins in 2020, then I think the Democrats will pick either Tulsi Gabbard or maybe Pete Buttigieg.