In order: Dead, dead, defeated and drained of all his power.
Being dead is not a problem at all in MtG universe. Elspeth and a few more characters can tell.
The real problem is like "We're running out of ideas again. Quick throw darts at wheel ! What did we got ? "Phyrexian" and "Tamiyo" ? Cool , let's do that . What do you mean Tamiyo is the least probable character to get corrupted ? What do you mean that basically mean the multiverse is fucked beyond salvation ? We don't care, look, phyrexian planeswalker !! Next time it will be Eldrazi Sliver Planeswalker !"
Well they did set her up well to be compleated. The trope of exposition of her good background in such a crapsack Multiverse as Magic is a red flag, to be honest.