I wouldn't overthink things. Revolving credit facilities like Tesla has are very common and typically secured. It's not entirely clear to me what "firewalled" means, but adjusting terms in the wake of a merger/change of control event is to be expected.

Tesla had drawn $678 million under the agreement as of June 30, and had several billion in assets (inventory, machinery etc.) pledged against this and various other credit agreements.

What some might not realize is that although Tesla are doing very well from a PR perspective, they are still massively cash flow negative, even at the operating level (i.e. excluding capex). Solar City is even worse (-$741 million operating cashflow last year and -$2.47 billion including capex).

These are numbers that any loan officer would be wary of.