That seems like a major roadblock, but hackers could imagine ways around it. Let's make it easier by assuming the creator can only store so many backups before running out of resources. That seems fair if simulations are anything like what we have now and restarting from scratch is unfeasible, perhaps due to lost input data or deadlines.

Then one approach would be to silently and irreversibly corrupt the simulation in a way that will become noticeable. Perhaps you fill every document with secret messages that require AI as smart as the sims to detect and is only revealed years in the future.

By the time it is noticed it's too late and removing all those messages will require more resources than the simulation itself. Trying to catch them on demand will require understanding how the brains of the sims work internally, which may be unfeasible.

That idea is probably preventable, but I'm sure there are exploitable and non-reversible security holes in any imperfect simulation.