Hello Jason
Strictly speaking, if the RTU license has expired, you should not use it, and should purchase the appropriate license to cover your requirements. If an audit is performed, the existance of an RTU license being used beyon its expiry date can incur financial and legal penalties.
Now having said that, experience has shown that during such audits, (if and when they do occur) auditors are generally leniant with such violations. They will typically let them slide, with just a warning or a request to resolve the violation. This will also depend upon the level of the violation, if it is say just on two or three routers, it’s probably not even worth their time. If it is on, say 400 routers then it may be that they will respond with some penalty.
Most forums will have posts with people having various experiences, and usually there is no problem. However, strictly speaking, Cisco does have the right to move against anyone that is in violation. So really, you’ll have to decide on what level of risk you’d like to take, and what the cost of that risk is. Does that make sense?
I hope this has been helpful!
Laz