With regards to licences, they will have access to the builder so long as you allow them to. You can either allow them to use your licence, or encourage them to buy their own, which is good for you, as it funds further development in Bricks, and good for them as they’re not tied to you.
With regards to handing off… I think I’ve noticed a rather polarised opinion across the userbase. Some think you should never pass off at all (and force a maintenance fee), and others just let the site go free. I used to be in camp 2, but it ended up being a headache, because I suck at charging for ‘bits and pieces’, and clients will invariably turn your creation into bits and pieces.
My final Elementor client has become quite proficient with it, which is both a blessing and a curse. Quite often I’ll be asked to go in and do a “quick tidy up” for mobile screens, which is, of course, a PITA because he’s been using pixels everywhere, with the occasional rem, hidden in a random breakpoint, just because he was feeling fruity.
I have recorded simplified tutorials for each builder, and provide it, along with the main documentation, as well as my prices for adjustments and maintenance with, and without my service plan.
I then provide an editor account, and an admin account, and install a user log plugin.
I warn clients that each price is doubled if the problem was caused while in the admin account.
Essentially, I don’t want to keep any information, or access away from them - it’s their product, after all… However I do make choosing my service plans seem like an incredibly good idea.
Generally, this seems to keep their involvement with the site to a minimum, and I get a regular income.
In return, they get to relax, use my licences (whichever have been used to build and maintain the site), WP rocket, premium backups, free hosting (some reseller deals are fantastic), site monitoring, and a heavily discounted “further design” rate.
If you’re not already, I’d highly suggest investing in a group of white label maintenance plugins/software/platforms, and not-too-gently nudge your clients into paying your a regular fee for maintenance and cheaper updates.