alt+F4 while playing HC

its dependent on the speed of your pc afaik and is probably not reliable. Exit and log in is almost always the safer option.

I dont have enough ram and alt f4ing gets me killed. I can more reliably hit the lot out button

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Can someone confirm that this will save your character 100% if you do it in time (if you see enemies taking no dmg or something similar)? Because I am not sure if it takes few seconds before disconnecting your character, or is it instant.

This is not "opinion based" or "guess work", it's all gathered from reversing the client and debugging it in real-time.

As of this writing, version 0.9.13i, "Exit to Log In Screen" is the safest and most reliable way to ensure you are disconnected right away.

When you choose "Exit to Log In Screen", the client executes a graceful socket shutdown process that is not called when you Alt + F4, click the X in windowed mode, or choose "Exit Path of Exile". Before that is done though, what I assume to be a "disconnect" packet is sent to the server. This packet is not sent by any other disconnect method either.

The "Exit Path of Exile" button executes most of the same logic "Exit to Log In Screen" does, except it closes the PoE window instead, and "Exit to Log In Screen" closes the socket instead. If the code were to be updated to close the socket before closing the window, as it should be implemented, then they would both be the same. That is not the case currently, however.

As soon as you click that button ("Exit to Log In Screen"), you immediately start the disconnect process, which the server can handle right away (see shutdown & closesocket for more information). Every other method to disconnect/terminate relies solely on the way Windows works as well as your connection to handle the disconnect.

That means for a lot of people, they won't notice it if their connection is fast enough (which changes how TCP operates in terms of internal settings) and their PC is fast enough (time for the process to shutdown is shorter). Then there will be people who do notice it, as if their connection or PC is not fast enough, the TCP cleanup can be delayed, which means their character stays in game longer.

That's about all there is to it from what I've seen. Hope it helps.