I wouldn't read too much into the fact that Towers haven't advertised for actors specifically for Sub Terra as normally the Resort put out a general casting call
for their Entertainments Team then allocate performers from there. However, I think what it will depend on is unforetunately what so many things come down to - budget. If Towers want Sub Terra to re-open, then not only do they need to allocate the money to ensure the techinal element of it is working, but also budget for the staff costs. Even if they run it with zero actors, they will still need staff in batching, baggage hold, safety checks, ops booth etc.
I wouldn't be surprised to see it perhaps open mid-season, however at the same time I also wouldn't be surprised to see it remain closed for another year. Whilst I've never been its biggest fan, it will be a shame if it remains SBNO for another season as it does work as a filler attraction and with the Resort now lacking so many flat rides its N:ST's abscence is all the more keenly felt.