I was confused when I read your topic title and thought you were replacing Bitcoin with something else. But upon reading your post, I realised you are referring to holding Bitcoin. In a short word, we should know to invest in Bitcoin that you can afford to lose. It doesn't really mean you have to lose; it does mean you might need to hold for longer to get profits as well, though anything could happen in the crypto market anytime. You should invest in Bitcoin from your savings, so you don't have to touch your Bitcoin for your life. Emergency situations are different issues; we can't predict them.
However, we always prefer to follow the DCA strategy to acquire Bitcoin. So you don't need to invest a big amount at a time. That's how you can build your Bitcoin portfolio, and your personal savings for emergencies will be safe as well. You should have a target for your Bitcoin sales; without a goal, you can't make profits.
I feel a little bit confused too upon reading the topic alone. You know OP, bitcoin shouldn’t be replaceable if you know how to manage and grow your bitcoin portfolio without compromising your savings or emergency funds. Bitcoin investment is not your emergency funds, rather it’s your retirement funds, that’s why long term investing into it is more encouraged.
Invest what you can afford to lose, without touching your emergency funds. Even if you lose your bitcoin investment, at least you won’t totally get broke because you have your own savings that will help you survive in the long run.