I didn't say he had 3.8 mana regen, I said the clarity gives him 3.8 mps. With his 0.9 mps at lvl 3, he has 4.7.

But even if he uses the wand charge he won from the dodged stun to use shards, what then? Both shards + snowball dmg after reduction leaves MK at 650 hp. You know how many hits it takes for Tusk to kill him then, considering MK natural regen? More than 15. MK hits Tusk for aprox 235 dmg after reductions, and at the start of the encounter Tusk has 639 hp (and he has only 0.8 hp regen per second). How many hits does MK need to kill Tusk? Less than 3.

If Tusk snowballed into MK, he ended up about 200 units away from him. MK has a 300 range attack. Tusk has 0.7 seconds turn rate, so even if Tusk decides to run immediately after the snowball hits (no shards), MK gets out of the stun 0.2s before Tusk finished turning, which means MK gets a free hit on Tusk.

Now Tusk keeps running, he has 365 movement speed and MK has 350, but he has phase boots so when active it has 434. And it lasts 8 seconds. More than enough time to chase Tusk and hit him 2 more times.

And there's no way Jakiro gets there in time to help.