When the btc mining process is over, how will the network remain secure as the computational power ceases to exist?
Still, a long way to go. More precisely, Somewhat 117 Years (+/-). Look at the picture below. I found it from the WO thread.
Here is a fun fact shared by hisslyness
Last Full Bitcoin to be added to the network will take approx 34 years (Approx. Block 5,168,390 -> Last Reward Block)
Max Coin Generated is 20,999,999.97690000 (rounding)
I don't know how the network remains secure after the end of the mining process. But, I believe mining is not going to end. They will get the transaction fees that we spend. A couple of satoshis will be worth a lot (I hope). I am not an expert on it. All I am saying is from my assumption.