Bitcoin rally today is huge and it must end at some point.
Now I want to swap part of bitcoins into alts with only one goal - to gain bitcoin value. What do you think? What alts will raise in bitcoin price in next days if bitcoin begin to fall in dollar value?
It has to end at some point, yes.
However it is unclear right now what effects that this eventual dump that will occur will have on alts. It could definitely lift altcoins up, basically the opposite effect that the bitcoin pump has done to altcoins yesterday and today, but it could also bring altcoins down with it.
Alts are indeed undervalued right now and whenever something is undervalued, eventually it will recover.