There's a 4 hour bus between Venice and Milan which certainly less than ideal but if you're interested I'd book early if the train is really going to be out.
From the brief announcements I saw it only affects the high speed trains. Have you looked into non-high speed trains?
On a day in the middle of August I see:
08:51 - 13:35 Venezia S. Lucia > Milano Centrale 4h 44min
Regionale 88755 Venezia S. Lucia (08:51) - Verona Porta Nuova (11:13) Regionale 2628 Verona Porta Nuova (11:43) - Milano Centrale (13:35)
If the outages only affect high speed trains this slower regionale should run fine.
The announcement says the the complete closure is just the fast train section from Vicenza to Verona. If you could book from Verona on you could bus or car service to Verona (much closer) and go on from there.
I do see available trains on the Trenitalia site offering alternatives - regionale to Verona and then the fast train to Milan or fast service Venice to Bologna then Bologna to Milan to route around the issues. Even if they cancelled your ticket it doesn't look like service is completely out. I would encourage you to explore the revamped options before throwing up your hand entirely.
Negotiating the trains in Italy are part of the adventure, but it looks like you might be the extra experience.
For reference here is the announcement I found: https://www.fsnews.it/it/focus-on/servizi/2024/7/31/lavori-infrastruttura-agosto-modifiche-treni-trenitalia.html
Good luck,
=Tod