Sometimes the convertible note is silent on this point, which would mean that the investor might simply get repaid the principal amount of the note plus interest upon a sale of company. I think that investors generally should have the right to receive a return greater than simple interest upon a sale of company before the next round of financing.
Savvy investors will negotiate for one of the following (1) a fixed or floating rate of return greater than simple interest (either similar to the conversion discount or something like 1.2x to 2x the principal amount), or (2) the ability to convert the debt into common stock or preferred stock at some pre-determined price (in order to capture the “equity upside” in the sale). There are some tricky tax issues for investors with regard to the concept of original issue discount, which I will leave for a later post.
I think it is generally unfair for a company to prepay the note without the consent of the investors in this situation, because this might eliminate the “upside” potential of the investors.