It would depend on how the unallocated shares are handled.
Let's say you issued 1000 shares of stock upon incorporation. It does not matter how we got there, but you end up with 1 person owns 500 of those shares, another person owns 250, and the remain 250 are still owned by the corporation itself.
When a corporation is "bought", the general concept is that some new entity is buying all the shares from the current share owners. They can do this with cash, or they can do it with stock, where you get shares of stock in the new company in return for your shares of stock in the existing company.
In your case you're obviously talking about a cash sale.
A corporation exists separately from the share holders. One person cannot really sell they company, all they can really do is make a proposal for all the share holders to vote on. Of course, if that person has a majority control position, their "proposal" is basically a statement.
So the person with 500 shares could sell HIS shares, and make a proposal to sell the unallocated shares for some net amount (we'll say $75). The person with 250 shares would end up with:
250 shares and no net change (there is just a change of control). This scenario is similar to what happened with Craigslist where an employee sold their 25% stake to ebay. Granted this was not a majority control scenario.
More than likely the first person was looking for some kind of exit, and the new owners don't want to be left with any hangers-on, so the "proposal" would be that the new company can buy back shares from existing share holders at a set price, and you get a check for $25.
Or it could be that the proposal is the $100 is divided among ALLOCATED shares, and you get $33.3 and the person with 500 shares gets $66.6.
More than likely though, it's none of the above. When you buy a company, you also buy that companies liabilities and commitments. Many times all that the acquiring company REALLY wants is the customer base, or some piece of intellectual property. So the "proposal" is basically:
Incorporate under a new name, with existing share holders remaining with the same stock
Sell the intellectual property and old company name to the new company for a set price (we'll use your $100 number).
You are left with: a shell corporation that has no assets or value (likely) BUT has retained any debt or liability. This allows the new corporation to expedite the "purchase" process without having to worry that they are inheriting some unknown liability.
As for the $100, the majority shareholder could "propose" that the entire amount be paid to him as a bonus of some sort, or could propose to dissolve the company and divide any assets among share holders, or any number of other things.