In the history of DVC, there was probably never a time of more "excessive borrowing" than in 1999, when OKW owners were told that reservations booked with points borrowed from their 2000 use-year would be include the "park pass benefit" that was due to expire on 12/31/99.
Even during that time, the system was able to run smoothly...
Except for the end of the contract - as others have mentioned - I can't think of a scenario that would cause them to suspend banking/borrowing...