It won't be put on the remaining legal target instead
That said, between ramps ubiquity in Commander, the fact that ramping one land for 2 mana has been good enough for many cards to see consistent play in the format for years, and the risk that Deep Gnome Terramancer will be a dead card is minimal at best, and Id call it a safe bet youll come out ahead far more often than not when playing this card
4 | Repurposing Bay Mana Value: 2U Rarity: Rare Type: Artifact Card Text: 2, Tap, Sacrifice another artifact: Search your library for an artifact card with mana value equal to 1 plus the sacrificed artifacts mana value, put that card onto the battlefield, then shuffle
Truly, the possibilities for a really strong deck with these cards is endless, but for players who like to Party, Garland at the Chaos Shrine looks like the best scene box to pick up.