Essentially, IPs are the address of any device which connects to the internet (phone, server, computer, printer, etc.). And when they run out, then you won't be able to connect to the internet unless you have one.
Since you probably don't have a static IP, your IP will sometimes be returned and you will be assigned a new one, if there are any still left. But don't worry, your ISP has a pool of them already reserved for you and your fellow clients.
The solution to this quandary is simple, change from IPv4 to IPv6. Notice how I said change? That's right, they aren't compatible with each other. If you change early to the IPv6 network, then you won't be able to view any of the internet as you knew it. Any site on IPv4 won't necessarily be online in IPv6. Everyone is waiting for everyone else to change - no one wants to jump in with both feet. So now, we're between a rock and a deep cliff: jump - or be pushed off.
Currently, 7 blocks of 16,777,216 IPs are reserved by AINA (these will be eventually released) and 5,731,~~~ are remaining. (In the minutes it took for me to write this, it is already down to 5,712,~~~)
What are your thoughts on the IPv4 and IPv6 protocols?
pax.