To my knowledge they can't buy on the open market except at times which they're deemed not to be trading on inside information. A quiet period would certainly not be such a period. On the other hand, if they have options that can be purchased at a fixed price, they should be able to convert them to shares and certainly would be able to do so if they're about to expire.
Some companies have very limited periods that employees can buy on the open market, but they're generous with the options employees earn each year. In IMGN's case, with the buyout, employees who had years before their options vested became instant multi-millionaires because all options became available immediately. I would imagine the same arrangement would apply here if the company were bought out.
Gary
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