Hi,
Your plant is a Kalanchoe, probably Kalanchoe scapigera.
Kalanchoes are a large family of succulents native to Africa and the Mid East.
as spituch has guessed they like dry conditions.
If you leave it in your tank it is most likely to rot.
And to answer your second question it is not good to have rotting plant material in your tank, Lots of bad bacteria.
Cactusdoug