First, I want to say, I do not think Marco can or will replace Pedey's offense, but I wouldn't say the "only way" about it.
1) Marco has been over .780 in both of his last 2 seasons at AA and AAA. While that does not mean he can do that at the ML level, it's not impossible to imagine him hitting near .790.
2) Pedey "at his worst" for a full season was .712 in 2015. He's 33 now, and one could imagine him declining next year. Plus, he's been under .800 in 5 of his last 6 seasons. That's not far from Marco's 2 season totals on the farm.
3) I wouldn't feel awful, if Marco had to play 2B a lot next year, but there is a significant chance he falls way short of Pedey's recent production. Pedey's at .764 now, and so projecting Marco to come close to that, I feel, is not a big stretch. They could both easily be near .750 next season.