Do Sales Insights Marketo Plug-in Licenses Expire?

We've sent licenses to a set of our Sales teams and it's been a few weeks.  I'm now getting a handful of requests for help, saying that their licenses aren't working.  It's as likely as not related to how long the license code is and them having trouble copying it, but I wanted to ask if there is an expiration period on these invitations?  Should they stay available unless I revoke them?

Thanks,

Jason