Seems the sale might be going till somewhere around 5/23-24. Minecraft sale page says merch is on sale till 5/24 but doesn't give a specific date for the game. Xbox and Win10 editions end date is around 5/23.
What's the difference between the PC(Java) and Windows 10 version?
Java Version: mod support, no marketplace (i.e. no in app purchases), can self host server for free
Java edition is the one sold on minecraft.net and runs on PC/MAC/Linux. AFAIK Java edition players can only play with other Java players.
Win 10: Better optimized/better performance, cross play with xbox/switch/mobile versions, must pay to host server.
Windows 10, xbox, switch, mobile all have their own compatible editions (called Bedrock edition). You have to purchase these individually for the platform you want to use, but they can play with each other. So someone with Win 10 can play online with someone with Xbox, etc.
Java Version no longer comes with free Win10 version, they must be purchased separately.