McGinn has a year left on his contract at Easter Road, coming off a season in which he scored six times and provided eight assists.
"John's value is in the team. If John doesn't go in the transfer window this season, I won't be disappointed", Dempster said.
"Neil won't be disappointed, the supporters won't be disappointed. We don't live and die by transfer fees.
"If we were to receive a transfer fee for a player of some significance, of course that would be welcome. That is balanced by the impact it would have on the team.
"John's a magnificent young player. I would be very surprised if we're not tested by a number of clubs."