I don't think a hostile takeover would work.
1- They would have to shell out a lot more to convince major shareholders to give up, and to force the buyback from the smaller investors (and as it is, Nvidia is worth susbtancially more than ATI, according to the current market cap).
2- Intel would risk loosing key people in management and R&D at Nvidia, as soon as the merger was to be completed.
3- The SEC and other regulatory bodies could see hostile buyouts from Intel as some kind of monopolistic behaviour, adding fuel to the Intel-AMD lawsuits around the world.
4- Intel is in the process of getting rid of anything that it's not in their core competence (chip design and manufacturing).
Having said that, i still believe it could happen, as AMD would not be totally helpless now, since they bought ATI.
Next stop, VIA buys S3. No, wait, they already own them...
VIA buys... Matrox