Nothing is a 100% safe including banks, bitcoins, and the building you are living in.
From an objective point of view, bitcoins seem riskier than gold. The instability of it is dangerous even if it can rise to levels. There can be better altcoins than bitcoin that would go to the moon.
The possibility could happen but with bitcoins it is already tested through times and it's the father of all the altcoins around so the any movement of the bitcoin would certainly affect the altcoins, on the other hand in terms of investment I agree that gold are safer but that is form long term investment while bitcoins you can maximize your earnings if you are good in trading.