It also depends on the amount.
My old PayPal went on negative balance for 170$ last year after someone scamed me and opened a dispute and won it (like always), and despite having money on the bank acc attached they didn't do nothing, no asking for the money, no sent to collections nothing at all... However if I try to login to that account now it says that something went wrong.
However I use a new PayPal with the same bank and name attached, received over 10k$ there and no issues at all.
I've heard that for large amounts they can send collections to get their money back.