It's clear to me that they pulled their forces back, as all of the Charr bosses that resided atop the pre-searing alter which initiated the searing seem perfectly fine afterwards when you have to fight them in post-searing as well.
Unless the Elric Brothers happened to pass by (wonder who'll get that) ^_^
Yeah, they passed through after drawing a few massive transmutation circles on the Bloodstones.
On topic, I think the expeditionary force is the best idea. Now that we've seen the REAL Charr army, the bosses who invoked the searing seem like NOTHING.