Change Technology of Theme

My templates were created with T3 framework and a generator of module types. I’m thinking about switching to Helix Framework and using a Page Builder. The questions are:
Can I submit it only as an update? (In this case I would keep updating for sites already created with T3)

Do I have to delete the template in Themeforest and resubmit it? In this case, would it be assumed that customers who have purchased the previous version of the template will be left without updates?

Thanks for the guidance.

If you delete the item, you can not submit it any more. You should use update option