if bitcoin goes up, altcoin will try to go up, and that also depends on how far it flies.
we can see when the last bull was in 2017 where the price of bitcoin at the beginning of the year 1000 $ then rose to ATH at 19k $.
altcoin had dropped, but then followed it.
in some cases there are a number of altcoins that even go up to 100x at the time of ATH for example XLM.
There were two incidence that happened during that time, the bitcoin value rose very high when the market players entered the market and at the same time, the ico became very popular then because of the rise of bitcoin, but the level of people in cryptocurrency then was still very low so the new broke fast and many people who are internet knowledgeable wanted to know about it, and from there they picked interest.
If bitcoin breaks forth today, don't be surprised that altcoin may still not follow, I mean altcoins that are below the top 20 in the market because many people are already used to this and they will not want to invest in altcoin again seeing how they have treated majority of their investors in the past, this makes me doubt if we will still have alts season.