What if you spend a week or month refactoring something that needs a quick fix now and is being deleted in 1-2 years? That's waste, and if you went rogue, it's your fault. Besides, you always create added QA burden with large refactoring (yes even if you have tests), and you should not do that without a discussion first--even if you're the founder.
Communicate with your manager and (if they agree) VP if needed, and do the right thing at the right time.