Yes, but frankly, C would still cause more havoc because even if the mainframes somehow continued to run, they would still be effectively inaccessible over any network.
We should not give too much importance to this, but the fact is that Python is now ranked consistently #1, #2 or #3 in sufficiently many rankings to consider it seriously.
That list is ranking languages by current popularity, though, rather than 'importance'.
I'd define 'importance' as more along the lines of "amount of havoc created if all software written using that language were broken/deleted at once".