My suggestions :-
i) Increase the HP and MP regeneration at the base.
ii) Make player to auto-select Mirana after respawn.
iii) Make the arrow doesn't hit the wards.
iv) Place something at the base that will attack enemies that entered. E.g, Fountain in DotA.
v) Show respawn timer.
vi) Pause the time when the game ends.
Hope suggestions listed above can be done. ;)
Nice map concept anyway. ;)