Getting a bit off topic, but what the heck.
I don't think the bell would allow the souls to return. The Sennadar gods only allow gates out of Sennadar (summoning demons is a different skill). So if a temporary gate was used, then Sapphire would get sucked out of Sennadar and the souls wouldn't be allowed back.
The plan was to get a gate out to the astral planes where the one and only gate INTO Sennadar resides.
That completely sidesteps where the gate originates from. Is it Sapphire performing the spell to recall herself to the bell, so gate is from Sennadar to Pyrosia, which the One is blocking, or whether the bell starts a gate out of Pyrosia and the Sennadar gods block it
The souls cannot return through to Sennadar, by the bell, unless the Gods permit entry through all gates, and they don't want to do that, because it was to stop demons coming through (if I remember right).
I think the issue about Niami twisting the other gods arms to leave the gate open for Tarrin, was for him to be allowed through the permanent gate. I'm not sure her arm twisting would get them to undo the blocking of gates in general ;)