They should have their shit together long before this. Have a flowchart and all variables there from the start. Nobody wants to start again from the beginning after hours of play. No sane person anyway. I patron games that will work with saves from like 2019. I've dropped patronage from several games that made old saves not work. Not hard to set it up so all that shit is set from the start. Remember the 7 P's. Prior Planning and Preparation Prevents Piss Poor Performance.
Just as a general heads up, if saves in a Renpy game break, you don't have to play through the game completely again.
The more choices there are, the more tedious it gets though to use these shortcuts.
Renpy has multiple ways to get to where you were.
Unless a dev deactivated the corresponding options, you can skip through the game by pressing Ctrl.
What exactly is skipped and what stops you from skipping further can be set in the settings:
(Default like this is skipping through known content and stopping at choices, so this activates where you want to skip in addition to that.)
You can also press Tab, which will automatically skip based on your settings until it stops, without the need to keep a key pressed. Ctrl gives you better control and skipping in bursts though in case you might want to stop in between somewhere.
Pressing Tab again ends the auto-skip.
Same if you click on the 'skip' button in the Renpy in-game menu:
Lastly, you can right-click the 'skip' button and get this dialog:
The advantage is, that Tab/the skip button actually runs through every screen and takes its time. That's great if you still want to skim through the story to remember, but not if you just want to get there without waiting some minutes in case of a more content-heavy game.
This option however literally just jumps to the next choice without context. This also means you can't scroll back here - because there is no rollback sequence generated by automatically running through the game.
It also means however that depending on the number of choices between you and the point you want to reach, this will be WAY faster.