Rita will get the most visceral impression of what happens, in the wake of explosion. Ignatius is helpless, pleading, desperate, but then something about Rita (and Strange's) responses seems to calm him. A sharp pain goes through him, like frozen ice in his veins, but in that moment he finds some manner of equilibrium - of understanding. He makes a decision, which he tries to impress upon her.

This is the last thing he can do, his thoughts and emotions say, without words. But... he trusts her. He trusts her with this. She's strong. Maybe she'll be able to do what he can't.

Then, his presence seems to shatter, in the same moment that the warm of his fire surges in her heart, like a secondary explosion of flame - almost too much to take, at first. Yet, as it spike of pain fades, she'll find that she's been left with a fragment of his power, a burning flame - the ability to act, where he couldn't.

In the same moment, his consciousness fades away from her, leaving the fire in her heart the only part of him left.