Well we know now.
We got our mail from St Brendan's Isle for the past several weeks and discovered that we had made the entire return trip from Marathon without towing coverage. TowBoat had sent us a registered letter before we ever left Marathon stating that due to the massive tow bill we'd rung up getting down there they were firing us as clients and including a full refund of our dues for the year.
I honestly can't blame TowBoat. We cost them several thousand dollars, and they did the deed in the most forthright way it could've been done.
It was an eye-opener though. I immediately thought of Rebel Heart and how they were a thousand miles out at sea when their sat phone service was switched off.
So now we're a SeaTow boat and I'm adding it to our predeparture checklist to call and verify towing coverage every day before we head out.