1. Grail doesnt connect to the Root. It's capable of reaching it, however.
2. Souls get recycled (however, this is implying Justizia, Illya and Iri even had a soul, which they don't, so you cant "reassemble them with the root".)
3. Nothing we know of can save Illya from her fate.
4. Grail gets deconstructed by Waver, Rin and the MA after the 5th war if it's not destroyed.
5. Grail wouldn't have prana to reach the root on Satoshi's 18th birthday. It takes the full 60 years, F/SN being the exception because the Grail got preemptively destroyed in the 4th.