I would check with your Business Partner, as long as you have a trusted relationship where they will give you honest answers. As far as I am aware, you have to have some level of maintenance to continue using the software starting with 7.x. The prior versions may be allowed to stop maintenance, but have all the caveats that you mentioned.
I have been told that if you drop all maintenance and need a patch or upgrade, you would have to buy the software from a new installation price point. I would get a confirmation that this would be the case in your instance.
Richard C. Browne, Jr.
Telecommunications Engineer
MAP Communications, Inc.