Can I come back after cancelling?

Yes, and your data is where you left it. If you cancelled under Settings and then Billing, your store is still connected. Once the plan has ended, opening nouz takes you to Shopify's plan page. A plan you choose there picks up where you stopped.

If you uninstalled nouz, install it again from the Shopify App Store and approve a plan. Your cost rules and product catalogue are still in your account. A fresh sync brings your order history back, and every order is priced the way it was before. Shopify decides whether any trial days are left. It counts the trial days a store has used in the past 180 days.

Direct customers billed in euro restart in Settings, under Billing. For them the free trial is once per account, so a restart starts a paid subscription at once. Between cancelling and restarting, Settings and Support stay open. So you can always read what happened to your account, and take your data with you.