These brain research techniques have now reached two key milestones:

1. They’ve found new ways to “fix” brain samples by filling them with plastic, ways that seem impressively reliable, resilient, and long lasting, and which work on large brain volumes (e.g., here). Such plastinationtechniques seem close to being able to save enough info in entire brains for centuries, without needing continual care. Just dumping a plastic brain in a box in a closet might work fine.
2. Today, for a few tens of thousands of dollars, less than the price charged for one cryonics customer, it is feasible to have independent lab(s) take random samples from whole mouse or human brains preserved via either cryonics or plastination, and do high (5nm) resolution 3D scans to map out thousands of neighboring cells, their connections, and connection strengths, to test if either of these approaches clearly preserve such key brain info.