Scenario A: 

Contingency: During migration.

Solution: Reactivate instance on old infrastructure. 

Outage Time: Minimal - only planned migration slot

Scenario B: 

Contingency: After migration a major issue occurs that would result in us moving back to the old infrastructure.

Solution: Migrate data back to the old infrastructure.

Outage: If only one customer affected within one working day. If all customers in a batch affected then 2 to 3 working days. Customers will be prioritised according to needs.