Hello, ​@Alyo!

When you’re using Manychat Free plan, you can have up to 1,000 contacts in your Manychat account. If your list is under that, you’ll be able to continue using Manychat Free plan.

Short answer: yes, if you delete all your contacts, you’ll be able to keep the Manychat Free plan.

One thing to add though, you cannot delete contacts in the Free Plan, you can only do that in the PRO Plan.

So you'll have to upgrade to Pro and then delete the contacts.

If you want to keep your costs down, the most viable option is to keep your contacts under the $15 per month limit, and pay only $15 per month.