Very much depends on your terrain (if you need gears) and if the conversion can be done easily (and cheap). In my experience, slush/salt isn't good but it doesn't exactly melt your chain and cassette. So even if you have to pick up a new chain and a slightly used cassette after two winters, it probably won't break the bank.

Not sure your experience riding MTBs, but it will be a dramatic difference from the Madone. You'll be noticeably slower.