Is there any issue with installing a Basic Security Suite renewal on an expiring Total Security Suite? I know I won't have access to Total Sec Suite features but is there any other issues?
There should not be any issues at all, just any features not licensed will stop working when the license for them expires. If you already weren't using them (or don't care about them) nothing will change.
You may see a warning that services have expired when you look at the firewall in Firebox System Manager or WebUI, but you can click to ignore that message.
WatchGuard Customer Support