what is Rasmus Ristolainen worth

Drouin for risto
More can be added to either

Risto would be a good fit for the Leafs if they could relieve cap space. Risto for Nylander but Buf would need to take on Zaitsev I'd imagine.

To tampa alongside Larsson and Hunwick for Callahan, Miller/Palat, and Sergachev/Cernak

anything to get rid of Larsson

That's horrible for TB.

Sergachev/Cernak > Ristolainen, cuz those two aren't defensively liability and are cost controlled for long period of time.

Miller/Palat > Larsson, this doesn't even need an explanation

Callahan = Hunwick, neither would even fit to TB roster, Callahan is the better player but TB needs to dump him somewhere