I do not profess to be knowledgeable in engine technology, but I would expect that running a Diesel at high hp output (towing) with a leaking headgasket would very quickly blow or melt a bigger hole through there, and start warping head or block beyond repair.

Can't imagine it'll get you very far once that starts to happen, and could leave you stranded with little warning, or lead to engine on fire.

If you know which cylinder is low on compression, and you want to squeeze a few more miles out of it, what would it cost to have a small shop install a new gasket just on the one side only?