I think it is better to sell them off before a few years. Depends on what currency. If they stand the test of time then definitely hold them for years and sell bits off when you happy with the price.
If you haven't already sold your ALTs simply hold if your project is decent. If the project has no future sell and buy into a decent project. This is all you can do to recover your loss without putting in more money. It will probably take a couple of years to recover your loss!
Some ALTs will never recover from this crash!
It is an ugly situation!
Who hold altcoins from Dec'2018 already in good profit. But in USD Bitcoin price of most important alts is far from the peak so holding them now is still good strategy. Maybe next few month will be altcoins month
Not really. It depends on what you holding and if you bought in 2018 Dec the price probably won't be up yet.