But he wasn't offering safe passage to Tevinter, he was offering indentured servitude for several years in exchange for his help. The whole mage rebellion is founded on mages being allowed personal freedoms, and yet Fiona would turn them into slaves just for chance of survival. Furthermore, do you really think that Ferelden would just sit back and allow a bunch of templars to attack one their greatest villages. No. Alistair or Anora would have gone to war with the templars and defended their wards. To leave them for dead or sell them out would have made them weak in the eyes of every nation in Thedas and would have allowed the rogue templars and foothold in their very lands. So while I may be empathic with their situation logic would dictate that they side with their Felelden allies then the Venatori.
I disagree. Yes I do believe Ferelden would sit back and let the templars kill the mages. Despite whatever Alistair's good intentions are, we've seen how his efforts to reform the circle even for his circle grey warden friend was overruled by the chantry and the templars. And Anora would have sold them out without even blinking. You think Ferelden who just went through a blight are willing to fight another war on behalf of refugees? Not all nobles are that noble sadly. at the time, she didn't know they were venatori who wanted to take over Redcliffe, just tevinters who wanted more mage servants. When Alexius took over Redcliffe well there was no turning back.
Indentured servitude was a better alternative then being slaughtered, that is the templars' justice for any apostate. That is the truth.