As an issue, fugedabowdit. I grew up in NC watching Jesse Helms on WRAL, which one minute spot vanished when he first ran. Reagan gave us a little over a year free from "Bedtime for Bonzo" reruns, and Pat Buchannan gave up a lucrative radio show in '96. Been there, done that, not a big deal.
Not to mention Alan Keyes and Lynne Cheney. And Al Franken. I'm sure there are many other people who left their broadcasting careers to run for office. It's not a campaign issue, but if NBC has a solid suit for breach of contract, it could give Thompson several million reasons not to run.