I don't  think you can check inactivity specifically but if you look in http://support.navyfield.com/Payment/OliveHistory.aspx it will show your payment history, including some event rewards. I think you cannot link steam account I just came back myself after a youtuber I watch (Ichase) made a video about the game. Actually got my old crews back and everything.
I have been quite enjoying the game after such a long break, I still think its more fun than world of warships to be honest. I was quite surprised to see the game still running.

Welcome back dude,

There is no nice way to link them, but what I did was download Navyfield from steam and just login when the game is launched. Steam version fixed a language issue I was having.

wow, me too

last activity was in 2013! wowie

none of my stuff is the harbor, sent in a ticket, hope they can find it!