Your 401 will be fine as long as you have a balanced mix of fixed income and bonds to compensate for the volatility of the market. I am a former Mead employee and I still have the Fidelity account from them. In my opinion the Fidelity offering is the best available. Low costs and a nice mix of funds to pick from. I wish you guys the best. Mead was a great company- hope that it turns out well for all.
To the extent you have your 401k is invested in MWV stock it's pretty much tanked. Even if you diversified it's probably taken a good beating. As far as your pension is concerned, unless you're at the very high end, it is insured by a government agency, the Pension Benefit Guaranty Corporation,(PBGC)which insures defined benefit pension plans similar to the way the FDIC insures bank accounts