I really don't see anything in O'Donnell that makes him every remotely worthy of being a Captain?. Just because he plays for Scotland means nothing that should conclude he should be given the captaincy. I don't see anything in the videos the club has produced or evidence when he is playing that he has taken on the mantle when Dec wasn't playing, not even slightly.
I would argue Kelly and Watt have done much more in dragging the club up from relegation not just with their play but their attitude and ability to get others involved around them. Watt was willing to play through an injury (potentially leading to being out longer) and come on score a goal and turn a performance around is a particular trait I would want in a player who wants to be captain. Someone who is willing to sacrifice themselves for the club to get a result amongst other things. I don't see that in O'Donnell.
I would also credit Kelly in turning our fortunes around at the back constantly talking to players and making sure the players are concentrating and cutting out mistakes, guy is non stop from the first to the last minute giving advice, guidance and kicking arse when necessary. I think this has given our defence some much needed confidence in the latter stages of the season