After a merger, the yield on mandatory convertible bonds remains the same and there is no reason to change it, unless the parties (the issuer and holders of mandatory convertible bonds) decide otherwise, since the yield on a mandatory convertible bond is an interest rate that is independent from the dividend.

However, the new basis for conversion is adjusted to factor in the exchange ratio. For example, if an mandatory convertible bond were reimbursed in 2 A shares and A was taken over by B on the basis of 3 A shares for 5 B shares, then an mandatory convertible bonds would be reimbursed in 2 x 5/3 B shares, or 3.333 B shares.