Every facility is different in that some will see traffic come back and some will not see traffic comes back. Heck, some facilities have already seen traffic come back or exceed pre-COVID numbers. That said, there is a lot that goes into a downgrade because of the money involved... and a fall in traffic because of COVID muddles the equation further. Remember, TCI is a rolling calculation, not a static calculation. As time goes on, and those COVID traffic count days are replaced by better numbers, TCIs should (theoretically) increase.
If there is a chance your facility will reach the TCI or TCI buffer to keep the pre-COVID higher level, you're unlikely to be downgraded. Why? Because a downgrade lets you save pay, IIRC, for two years. And when that traffic comes back to pre-COVID levels, they will owe you another 6% (or 8%) pay raise or the bottom of the band, whichever is higher, for the upgrade.
For all the craziness that is the Agency, even they are not crazy enough to downgrade a facility, where folks save pay... and then turn around and upgrade that facility back to where it was pre-COVID while providing everyone the CBA increase in level pay raise.