Hmm...the rest is 2' tall grass?
You need to bale that shit, not cut it.
If you do "borrow" a lawn mower plan on buying a new one to replace the one you kill trying to "mow" with.
Just to stir the pot a little. How do you know that the sellers stopped paying for lawn service? For all you know maybe they dumped their money pit and are now on a cruise somewhere celebrating getting out from under it(the reason they are unresponsive to inquiries) and maybe the lawn guys were hosing them. You said they do live outta state after all. Not like they were around the corner keeping an eye on the place 24/7.