[DanielHB]

The limits are when companies and institutions start to default on their loans. Or, in the case of governments, trigger hyperinflation by printing money to pay off the debt.

Of course it can collapse before that, but if it gets to that point it is guaranteed to collapse.

[jimnotgym]

But that won't happen while the share price keeps going up no matter what. Borrow more, secured against the massive unissued equity, or issue more shares.