No, but if Lara did demand it as a favor it would put both Mab and Harry between a rock and a hard place. Depending on the politics and guilt of Thomas, releasing Thomas may blow the Accords apart.
I don't think the Svartalves are that important of a nation, really. Rescuing Thomas
during the talks was a potential disaster because if it had become known, Mab's representative was breaking the rules at a major diplomatic meeting for Mab's Accords.
Now that that's a "fait accompli" I think the political picture is different.
The larger problem is that if Thomas was just released from Demonreach now, he'd die. There needs to be a solution for the whole "Hunger eating him" aspect first.
Also if Thomas was guilty, would Alfred obey Harry?
Yes. As Alfred says, "YOU ARE THE WARDEN". Harry could release all kinds of things.
That's why it's such a big deal among those few people who know about it... the Warden of Demonreach could basically cause a PT/BG level disaster any time he felt like it by releasing some horrible monster or ancient titan.
Which is one reason I think the 'kicking Harry out of the Council' bit is a ploy.
We know he'd never do it, at least short of a Changes-level situation, but the people on the Senior Council who still think Harry is a potential ticking time bomb... given the binding power of oaths, he could just extract an oath from some titan to kill all his enemies on the Council and then release it.