I don't believe the merger is likely to go through. Cadence and Mentor have significant product overlap. Their customers are locked into specific product design flows and it is not easy to migrate these design flows to a new platform. So, Cadence will have to either continue to support the existing products for the foreseeable future or attempt to force customers to go through an expensive transition.
Cadence is planning to take on significant debt ($1.1 Billion) to finance the takeover. This is reminiscent of the Daisy / Cadnetix merger when Daisy had taken on $200 Million debt to acquire Cadnetix and the debt payments ultimately doomed Daisy.
Most importantly, markets spoke yesterday, driving down Cadence stock 6% -- so the Cadence stock holders saw $150 Million of their market cap disappear. If Cadence were to give up the pursuit of Mentor, Cadence stock holders are likely to see the stock come back up.