last resort
The only remaining option that may help one or be of any use after all other options have been exhausted. I didn't really want to ask Mr. Stadler to write my college recommendation, but he's my last resort at this point.
last resort
A final expedient or recourse to achieve some end or settle a difficulty. For example, If you don't improve, we'll try this new medication as a last resort. This term originally referred to a court of law from which there was no appeal. [Late 1600s]
(as) a last reˈsort
a thing you decide to do when everything else has failed: Nobody wanted to lend me the money. As a last resort I asked my brother-in-law, and luckily he was able to help me.