What if there's an injury?

That's Hockey players get injured and we have Anderson, Korshkov, Barbanov & Liljegren, Dell to call up if need be.

If it's short term how do you have cap room?

Palmieiri alone is worth a B prospect and 1st, or A prospect and later pick. For Palms with the salary retained, its A prospect + 1st.
And McLeod is would similar NHL-ready young player (such as Dermott).

In other words, it would have to include a prospect, such as Robertson or Sandin.

It was reported at the Trade Deadline that all 8 Canadian teams were on Kyle Palmieri's no trade list, Reportedly he doesn't want to play in Canada. So i don't see him waiving for any Canadian team.

That trade Palms is not good enough anyway

No from Isles as they do not have the cap space to sign Mikheyev unless you want to take Komarov back.