In most states, it will be very much related to the old company's experience rating. This has been thought of and tried for many years, in every state. It is called "dumping" or SUTA dumping. Businesses are sold and change hands or reorganize all the time. How lovely it would be if you could restructure your business, close the old one and end up with a bright shiny new employer account without the high experience rating your old business has accumulated. Doesn't happen. Employers who buy a business or reorganize a business and lay off all the old business' employees will usually find themselves not with a clean slate and a low experience rating, but with the experience rating of the former business. In most cases, you buy this along with the rest of the purchase, or carry it on through the reorganization. If you want accurate details related to how your particular state deals with this issue, I suggest you call the unemployment tax unit of your state's Department of Labor (the same ones you submit your wage records to quarterly.) They'll be able to tell you just how it works in your state.
But you're using the new business, the buy out, whatever you want to call it, as a time to clean house. That's as good as it gets. You're not able to "punish" these marginal employees you want to get rid of any more than by letting them go through no fault of their own.
If you try to terminate them for cause, bringing up "performance issues" or any such manufactured excuses for why the old company's account should not be charged related to their being let go, it will be dismissed and they'll be approved quickly. The business has kept them on for an extended period, and suddenly decided their performance was not up to snuff, just as they were being sold or restructured. So you're not going to be able to show a clear valid trail of disciplinary measures for their supposed poor performance or a pattern of job related misconduct, and they'll be approved to draw benefits anyway.
If you have a poorly performing employee, discover that you have made a "hiring mistake," it's good to get rid of them quickly. This way, though you will have only a tiny liability for unemployment, or perhaps none, if you move quickly enough, you'll have a clear cut performance issue/tardiness/attendance/insubordination problem. They may get to draw anyway, but it won't hurt your bottom line much if at all. If you allow marginal employees to languish in your company for years, not dealing with the problems proactively, then you'll end up with probably not enough of any one issue to terminate for without having to pay unemployment benefits, all of which will be charged against your account. If they were good enough to keep for five or six years, it's then much more difficult to come in and try to show a misconduct reason for termination related to "they weren't doing a good job" or anything else.