The first name that instantly comes to mind is Callahan because there's no one on the team more qualified than him to the captain at this point. His record speaks for itself. You could name him the next captain of the Lightning and no one would bat an eye and it would be hailed as a brilliant move. Some might say "why not one of the younger kids?" and while that's a good argument, this is a young man's team. You need a chief, not one of the Indians wearing the C. He's my go-to if Stamkos walked.
But there's a few other routes we can go.
Hedman is 2nd in line for me. He seems to be a "do as I do" player as far as I know. But truth be told I saw enough of that with Vinny and for all years he was on the Lightning I don't know of any anecdotes of his leadership ability. Through the media we heard that Richards and St. Louis were the "rah rah" of the locker room. Your captain doesn't have to be "rah rah" but I'd expect him to be the one who gets up on the benches and says "EVERYONE LISTEN NOW!" in Game 3 of the SCF and you're down 2 goals after the 1st period and already trailing 2-0 in the series. I don't know if Vinny ever did that stuff or not. I don't know if the mild mannered Swede with the permanent smile on his face would do that.
Hedman would be a great choice but not for the best reasons. They are 1. He's been here the longest other than Stamkos 2. The players rally around him on the ice. Other than that I have NOTHING else to go by though.
Filppula is an outside the box choice but to his credit he's won the cup, he's the most well rounded player on the Lightning, he's a veteran and is a model player. But I can't say I've ever seen him spark the team the way Hedman, Callahan and Johnson do.
Johnson is another choice because he's a phenomenal player, the team loves him, you can see him constantly talking to everyone on the bench and is even a little feisty and in your face to other players without starting a fight. If Callahan wasn't on the team I'd say he was a good pick. But appearances are everything and I don't know how seriously a captain Johnson would look to other teams.
Ditto Palat
I think for now we need to put the permanent A on Callahan and if we still do 3 A's then you rotate Boyle, Palat, Johnson and Hedman between home and away games as the other alternates.
The most assuring thing is that there's so much leadership on this team that you won't have to look far for a captain outside of Stamkos.