LOL. As if people of all times in history hadn't been aware that serving a god was, at best, a mixed blessing. People were in fact rather more practical and world-wise in these things in most real-world religions except for the monotheistic ones. I bet that if you asked the typical Dalish Keeper how you should decide, they'd say "It is a path you can choose, but think very carefully about it. The reality of serving a god in this way is rarely what you think it is."
Do we live in the same world, I wonder... Seriously, so many religious zealots everywhere in our days with science on guard, with skepticism as a general rule of guidance, that I gave up for any sense from modern humans. And you expect someone razed in believes and who suddenly got absolutely undeniable proof of god's existents (I mean the whole temple) to refuse a god?
I would not bet on Keeper's reaction or rather think a Keeper would take that boon to itself (as an elder and obviously more worthy then you). But reaction of a "typical dailish" you could clearly see in DA2 when Merrill met Flemeth. THIS is normal reaction - bend your knee and obey. You already serve - it can not be otherwise. All you do now is getting huge power (only developers really know what is this power exactly but "power") and become a very personal servant of your beloved and "worshiped-your-whole-life" goddess What is not to like here? And how can you give THAT to anyone else (yet alone a shemlen).
Sure, for humans (dwarves, qunary) it's different. But for them the key word is "power". And if at some point your inquisitor believed to be chosen by Andraste (and absent-y figure as well as the Maker), to be the chosen one by another god - is it such a big step? Especially considering real power on your hands?