Yes. In the very beginning of the Bitcoin project there were long gaps between blocks that suggest that no node was mining/online at all. E.g. between between Block 27 and 28 there was a 8h34 pause.
Block 27: 2009-01-10 06:56:13
Block 28: 2009-01-10 15:30:57
I would guess that in the later years, there was never a time when you wouldn't have been able to get blocks from another node, except if you had been disconnected from the Internet yourself.
The only likely possibility that I see today for nodes to be online but unable to synchronize with the blockchain would be if the internet were to be completely disconnected between continents or nations for a time, also known as netsplits.
Silly thought: Even then, synchronization and confirmations could be achieved with largely increased latency when the blockchain data/transaction submissions would be transported via physical media e.g. pigeons with a USB stick. You shouldn't trust zero-confirmation transactions while being split-off, though. ;)