You'll definitely get the put assigned. Assignment depends not only on where the stock closes, but also on what it does after hours. If I had a Tesla put Friday after 4:15 PM that went ITM, I'd simply short the underlying and exercise the put, collecting the delta. I would do that until the exercise cutoff. But how bad is it really? A $10 move of 100 shares if $1000. So from 419 to 390, that's $3000 which will be partially offset by your short shares. Probably best to just close the position and move on unless you are bullish in which case sell a call until you lose the shares.
How bad? My guess is that the guy shorted 50 of them at 0.3 for $1,500 in premo. He's not freaked out from a one lot. 90% of naked put sellers do not have the capital to take possession of the shares. It's why BDs like IB will automatically buy them back at mkt 15 minutes before the close if you are not cash secured if/when assigned.

