Hello! Here to add on that yes, the saves are deleted after you reach the "correct" ending for any case. This is so that you're forced to start again from the beginning (to trigger another case) and lowkey manually perpetuate a time loop.
You SHOULD be able to skip through anything you have seen before. I'm not sure why it would prevent you from doing that.
But in the off-chance that you would like to try to get the true end/different case, you can toggle the skip "Unseen Text" in the preferences to True.
I have written stuff in to stop skipping when you've reached certain sections. (Like the end of the Prologue for example.) So even with skipping "Unseen Text" you should still be able to get back to the new content. As long as you don't have skip "After Choices" turned on, it should give you breaks to stop skipping.
Thank you for playing the game though! Other than the saves/skips I'm glad you enjoyed it!