Provided that you are competent on instruments then without a doubt your safest option would be to climb to a safe height, call for help and plead force majeure. As you say, expect a chat with the senior pilot and a few lessons on how to plan a flight using the current meteorological information.
I would emphasize though that you should be competent on instruments. Yes a lot of accidents due CFIT but quite a number with pilots not able to fly IR due a lack of training, the late John Kennedy jr. springs to mind.