The only argument that makes Connor seem manageable is that any attack on the village would require fresh bodies to be animated. Most will have been burned by the villagers after surviving the night, so that swarm of undead will have been curtailed (though in the final sequence they're busy wasting boats as funeral barges, so some dead remain). So the demon would have a smaller attack force this time...
Otherwise though it's not as if the demon is defenseless. It can mind-control Teagan apparently which is a major setback for the idea that Teagan can "keep Connor under control." We can't know at that point that the demon has plenty of spells in its arsenal, but it wreaked havoc on a fully-equipped and manned castle, bringing it to its knees. So Isolde and Jowan will beat demon-Connor and charmed-Teagan? Yeah, no.
And to repeat, there's no reason to trust Jowan at all, even if you're peaches with blood magic and were his friend in the Tower. His assassin role was bad enough, but a Tower Mage will have witnessed his freaky blood magic stunt during which, as a "friend", he leaves you behind to suffer the consequences of his escape.
Not to mention several other variables for going to the Tower for help. They mention the trip across the lake but the map doesn't show a quick water route, and the risk of being waylaid on the road and killed remains. And even if Irving owes you a favor you can't know he'll grant that favor- or even be able to after the decimation of the Tower and most of its mages. And if you're a Tower Mage and haven't returned to the Tower yet, you can't know you'll even be listened to. And if you're not a Tower Mage you also can't know in advance what kind of reception you'll get there at all. So you're not even guaranteed success for risking Redcliffe again. And after all you'd done to save them, what a risk it is.
And even after you get back safely, Connor still passive upstsirs, you risk a Mage being killed in the Fade while single-handedly taking on a demon in its own domain. Of course, their death means The End for the game (ridiculously), but ostensibly it just means sacrificing someone valuable to saving Ferelden- perhaps yourself- (though perhaps Jowan doesnt count) for Connor and then having to kill Connor anyway.
And as I also mentioned before, if you go with Jowan's blood magic ritual you don't have to travel but you're guaranteed killing Isolde and again risking a valuable Mage.
No, the most prudent roleplaying response there- the only option guaranteed to minimize losses and get a quick, sure resolution of the demon problem- is to immediately kill Connor and get going with the arl-fixing. People are dying! Hehe... But I've still never gone that route... (except once just to see what would happen and reload...) So I'm off to save the Tower, the wonderful Tower of Oz...