My father has moderate dimentia. I am concerned with the financial implications of his assets with finding a facility to care for him.

A facility will never take over all of his assets, however, his assets may be used, on a monthly basis to pay for the care that he is receiving.  If you have found a facility that is affordable to him on his monthly pension and social security, then you will have to devote those assets to his housing.  If he requires more care, you may have to use other assets, as needed to pay for that care.  however, as I said above, a facility will never just take over an asset.