Actually, whether our navy was destroyed on the turn or not is irrelevant, because the turn hasn't been done yet and will be influenced by our decision.
On the attack itself:
Morovia is currently only reachable by sea, or by going through UnNaCo. That are, basically, our two possibilities.
a) Attacking by Sea: We need to build up our navy, cannot use our torpedo boats and have to do a landing under enemy fire and probably upbuilt coastal forces. Afterwards, we have to secure logistics, that is ship routes, to transport ammo, fuel, ... Also, we'd (after we'd win) enclose UnNaCo, which for them would be a pretty good reason to attack us.
b) Attacking over Land: We use our current Army, which at the moment isn't occupied. They, using ground support, will probably strike pretty deep into the enemy's ranks before reinforcements (in the form of Morovia's army if they ally) arrive. This will form a single front with two enemies, with UnNaCo's army decimated.
if the surprise attack succeeds, they will also have lost much of their navy. If it doesn't, we still can advance outside of the coastal bombardment envelope, and attack with torpedo bombers. Plus, for Morovia to actually attack us with PT boats, they have to move through UnNaCo's coastal waters.
Basically, the problem is as such (excuse my crude drawing skills).
a)
b)
If we attack them directly, the worst case if for them to work together, in which case there'll be one front which we can supply and support directly. Plus, of course, naval attacks which even without the surprise strike we should be able to use our coastal guns and bombers to defend the coast.
If we attack over sea, the best case is a single front we have to supply over seas (with the enemy subs), the worst case two fronts.