Will my old complaints or grievances just disappear once new management takes over?

Not automatically, though how they're actually handled going forward can genuinely depend on what stage they were at and how they were documented. A complaint or grievance that was already formally raised, investigated, or resolved before the sale doesn't simply vanish from history because new management arrives — records of what happened, and any commitments made in response, are part of the business's history that a new owner generally has access to and, in a unionized workplace, may be bound to continue addressing under an existing grievance process.

What can get lost in practice is momentum and institutional memory — a complaint that was informal, verbal, or still being worked through can genuinely stall if the new management team simply isn't aware it was ever raised, especially if records weren't transferred cleanly or the people who knew about it are no longer involved. That's an administrative risk, not a legal wipe of your rights.

If you have an outstanding concern that hasn't been resolved, proactively raise it again with new management directly, referencing when and how it was originally raised, rather than assuming it's automatically being tracked, and keep your own copy of anything you submitted originally.