IMHO support agreements are very simple: either you pay for support, or you don't. And it's an all-or-nothing affair (CALs are always included).
If you stop paying support, you're not entitled to upgrade to versions that are more recent than the termination date of your support agreement. But in my experience, the next SR won't make any fuss about that. As long as you don't try to upgrade to the next major release.
What do you mean with "How does this affect the assignment of the CALs?" AFAIK ending your maintenance agreement doesn't.impact your CAL assignments...
Depending on who your Qlik supplier is the 'Support' and 'Maintenance' may be two separate items.
Support of your applications, and/or maintenance cost for the QV server and CALs.
If your looking to end the 'Qlik maintenance' then you should follow Peter C's post, and also be aware that if you need to start official Qlik maintenance again in the future then there may be a penalty to pay, in addition to the maintenance cost.
Best to clarify this with your Qlik partner to help work out the best options for you.