Yes Penny is MUCH easier to bring back all they need is a local copy of her memories and a backup body.
As for Pyrrha they cant go too long because interest will wane.
Most likely by sometime in vol 5 they will either hint or stinger Pyrrha's return.
With her full reveal in vol 6 that way they bookend it.
Her "death" in 3, her reveal in 6, and then her return in 9 with 12 being the final volume is the idea I have been working on.
For Penny though there is a LOT of ways to play it from her not having knowledge of RWBY to her not recalling the tournament because her backup was too far back and so its from those times.