1 bitcoin worth 500k USD or 1 million USD is not a barrier for anyone who wants to invest in bitcoin because no one forces you to buy full 1btc. Like you are now, are you buying full 1 btc per purchase, or are you also accumulating Satoshi every day?
Our goal of investing in bitcoin is profit, so as long as bitcoin still has profit potential, even if it is worth $10 million, we still have to buy it and wait to sell it at a higher price. When investing in bitcoin, we need to care about what price to buy and sell at to get the best profit. Don't make the excuse that bitcoin is too expensive and we can't invest in it.
Realizing this as soon as possible makes someone do a lot better. I understand that it may not feel all that well to invest into something that you think bubbled up and could burst at any point, but it is also true that anytime bitcoin has gone up, it has managed to go down eventually as well, that is why it is so important.
I believe that the best thing to do would be keep buying and holding long term, if it ever passes 500k then we already made 10x return which is great, but even if it goes under that price after a while, I bet that if you hold it long enough then it will keep growing. These are all important stuff that we should keep doing, that is how we make some money from it. I believe that it will be quite well without a doubt.