Illness as he had suspected. The only part of Strange's story he takes issue with is the 'greatest mage' part and for the first time in their conversation together, Solas decides not to immediately bring this up and bites his tongue.

"You are not worried she will be sick if she is resurrected?" A big 'if.' Solas may be guiding Strange on a quest, but he has no real intentions of helping him in such a foolhardy mission. He had his own to work on.