I have his ceiling at somewhere around 20 goals/50 points, but a lot of it depends on his role. He's that rare kind of swiss armyknife who can fit into basically any role. You want a defensive responsible center who kills the opponents top line? Here's Girgensons. You want a checking forward to shake things up? Here's Girgensons. You want a big power forward who drives the net and scores and opens up space for his linemates? Well, here's Girgensons.
Long story short, I thing Girgensons value is higher than his production.
Solid synopsis. He's versatile and responsible, what remains to be seen is how Buffalo use him going forward. Wing may open up more offensive opportunities for him and drive higher production.