I don't think it's at all far-fetched. Macromedia is a relatively small company and has suffered some serious losses over the years. If not MS then possibly someone else. Stock price has been rising steadily (from $7 in 01-Oct02 to $13 today).
On the positive side, MS is antitrust shy and Macromedia has weathered storms before. As others have pointed out, this is an old, recurring rumour. The outlook for 2003 is much brighter than last year. 3rd quarter 2003 results are due on 22 January 2003.
Yahoo Finance: Macromedia
And yes, it would suck.