Yes, there are reports Mika is in discussion with BAR, but to be honest, I'd be very suprised if he went from a 3 year sabbatical, STRAIGHT BACK into an F1 car.
A lot has changed in those 3 years, for him, as well as the sport itself.
Webber I believe, will get 3 seasons MAX to deliver a WDC to Williams. Frank Williams and Patrick Head are the biggest hard asses in F1, and they never allow their drivers to fail to deliver, which would explain the 'relative ease' in which they got rid of Ralph and JPM.
I believe they have a decent package for '05 - and with Webber, and more than likely, Button, they can give Williams it's first WDC since JV in 1997.
Button to Williams, while not 100% confirmed, will happen. No such thing as a "bind proof" contract anymore .. money always wins out, and there are always ways n means of getting out of any contract. In my oppinion, Takuma will stay at #1 driver for BAR Honda next season, and I am sure Anthony Davidson will go to #2 driver.
Personally, seeing Button, arguably BAR Honda's best driver, in the short few years they've been in F1, leave the team, the way he has, is heartbreaking.
I would like to either Nick Heidfeld, or Jarno Trulli step up to BAR tho.