Assumptions:
1. John is still living, albeit with dementia
2. Mary is in the full of her health.
3. Adult off-spring are also in the full of their health.
Scenario 1.
John passes away.
Will is executed, Mary / beneficiaries inherit.
Scenario 2.
Mary passes away.
Ward of Court application likely needed to handle John's affairs.
Will is executed, John / beneficiaries inherit.
Could also make Ward of court application now - might make things simpler.
Have I missed anything?