Ok, this is the data that BMI have failed to communicate to us, but has appeared on FlyerTalk.com (Emphasis mine).

• First stage (legal exit from the Star Alliance) will effective from 17th April 2012 (TODAY).
• Second stage (customer benefit end date) effective 31st May 2012. This will include, but will not be limited to, the following changes:

• End of Star Alliance mileage accrual on bmi operated flights.
• bmi DC members will no longer accrue mileage on Star Alliance operated flights.
• Priority reservation, waitlist and standby will cease for Star Alliance customers on bmi and vice versa.
• Priority Check-in, boarding, baggage delivery will cease for Star Alliance customers on bmi and vice versa.
• Additional baggage allowance will cease for Star Alliance customers on bmi and vice versa.
• Lounge access will cease for qualifying Star Alliance customers on bmi and vice versa.

The marketing and product development teams are currently outlining the new customer offering and will let you know the new bmi (non-aligned) product description in the forthcoming weeks. Please note that bmi will be a non-aligned carrier as it will not join One World.

Lets put this into a list of dates, then deal with the OneWorld thing… (thanks to aidanc for the original) – I’ve just added a bit of clarification and emphasis.

• From 19th April, no redemptions on Lufthansa family/Miles and More airlines – that’s Lufthansa, Air Dolomiti, Austrian Airlines Group, LOT Polish Airlines, Swiss International Air Lines ,Adria Airways, Croatia Airlines, Luxair, Brussels Airlines and Germanwings
  
• From 19th April, no changes to  Lufthansa  family redemptions
• From 19th April, cancellations of Lufthansa family redemptions possible for the usual fees, points returned

Now based on the data above and other information:

•  Until 30th May, Star Alliance Gold  benefits apply except on Lufthansa family airlines
•  Until 30th May, Star Alliance redemptions should possible except on Lufthansa family airlines

And regarding British Airways:

• Post 20th April, they BA/bmi are working on a new customer offering
• Post 20th April, this offering will include some form of BA (metal) earning/redemption, but has not been announced

But lets turn our heads back to BMI NOT joining OneWorld. That is a touch… worrying.

Now, if British Airways decides to absorb BMI completely which is the plan, hopefully there would be some Diamond Club to Avios match. There are questions to what a BMI Gold or Silver would be worth within and beyond BA land from 31st May. Hopefully we’ll know more on the 20th (Friday).

My advice remains the same:

REDEEM THOSE MILES. NOW.