I think we have to try our hardest to keep Barnes and Iheanacho. I know its a tough ask, but these two would be unstoppable in the Championship.
As for players to leave, Tielemans, Cags and Maddison well all know will leave. Castange will probably leave and Mendy out of contract (although I would give him another year as well as Evans). I'd try and keep Praet as well, he could be the player to make things tick for us. I would get rid of Vestergaard, Betrand, Amartey and Perez.
Players I'd like us to bring in if possible would be Kent from Rangers, Brereton Diaz (if we could), Alex Scott from Bristol, Jack Clarke from Sunderland, a CB, two CMs, and another LW and RW. I'd also be tempted with Langstaff from Notts County - think he would fit into our team really well.
My Team would be
Iverson
Ricardo/Justin
Souttar
Faes
Thomas/Kristensen
Ndidi
New CM
New CAM
Barnes (obvs if we can keep him)
Iheanacho/Vardy/Daka
New RW
I would also bring some youth team players in like Brunt, McAteer, Maswanhise, Madivdua, Braybrooke and Alves.
It will be tough, but I think we will do it and come back up!