Sure you can keep your HK investments. But if you are living in Germany they you will be paying German income tax on any HKD income received in HK on those investments.
I'm currently considering to move to Australia, but keep working remotely for my HK employer and receiving a HKD salary into my HK account. Now I live in HK, I pay HK taxes which are around 15%. If I move to Australia, I will need to pay Australian taxes on this income which is up to 45%. So I'm going to be a lot worse off financially. Luckily there is double tax treaty between HK and Australia which means I will not be paying 60% tax (15% + 45%), but I still have to pay the higher of the two which is 45% (15% to HK government and then this can offset what I pay to Aus government so I only have to pay 30% tax in Aus). But still overall I'm going to be paying 45% tax on my HK income next year which sucks but at least I will get Australian medicare and other benefits, and my kids will be able to go to an Australian government school. So I'm almost ready to pull the trigger.