After weeks of being in sync and working fine, my Geth just stopped. Upon restart, what started as a long hang on FS Sync Time (repeat output with different values, no further movement beyond allocation of cache and file handles), turned into a panic on latest launch:
INFO [03-17|12:07:14.213] Initialising Ethereum protocol versions="[63 62]" network=1
WARN [03-17|12:07:15.325] Head block missing, resetting chain hash=5414aa…aaf1f5
WARN [03-17|12:07:15.325] Rewinding blockchain target=0
panic: interface conversion: interface {} is nil, not *types.Block
goroutine 1 [running]:
github.com/ethereum/go-ethereum/core.(*BlockChain).CurrentBlock(...)
/home/travis/gopath/src/github.com/ethereum/go-ethereum/core/blockchain.go:359
github.com/ethereum/go-ethereum/core.(*BlockChain).SetHead(0x400c4aa000, 0x0, 0x0, 0x0)
/home/travis/gopath/src/github.com/ethereum/go-ethereum/core/blockchain.go:302 +0x8a0
github.com/ethereum/go-ethereum/core.(*BlockChain).ResetWithGenesisBlock(0x400c4aa000, 0x40002d4120, 0x0, 0x0)
I am now unable to progress past this point.