But, what if Bitcoin never reaches a new ATH? Then, I'm afraid that most people "hodling" Bitcoin will lose all of their investment in the long run.
What are your thoughts?

No new ATH would mean not much further evolving of Bitcoin - as technology and as acceptance/use too. It would mean Bitcoin dying. It would make the miners leave. It would be bad.
But I don't think that this can realistically happen.
Also, how many years means "never"?!

For me it is not possible, bitcoin will surpass its previous all time high but it will take time. But if the bitcoin will not achieve the new all time high then it means that the demand is gradually decreasing and the buyers are overwhelmed by buyers. As time passing by technology become more advanced and we humans need improvement and for sure that there are many people who wants to adopt bitcoin.