This is a very complicated question, several answers to it, because the departure of the client may be due to reasons of a technical nature on your computer, and server crashes.
For, to eliminate technical reasons on your computer, check the following.
A computer must meet the minimum technical specifications. If the specifications of your computer are worse, than declared for EU, switch to High modes, Medium or Low T.P. in the graphics settings.
Communication — usually, main reason for departures. The computer must be connected to the communication channel (to the router) wired and should not share this channel with other applications, in particular online movie watching and any data streams.
Do not play via mobile internet, via WiFi channels, to which other users are connected. Even in case, when your router’s declared WiFi bandwidth is 300 megabits, if 3 clients are connected to it, you will already receive 100 megabytes for your computer, of which 50, 50.
Routers also tend to adjust the band at different loads, so, if the router has the ability to configure QoS (Quality of Service), configure in the router the maximum priority for the IP of your computer (in this case, this IP should be made static).
Perfect option — wired connection, QoS for your IP address and no movie watching online. Online radio usually does not interfere, but if the communication channel is not very fast, try to do without radio.
If all these conditions are met, but departures continue, set the connection speed in the settings (in the lancer, before loading the game) speed 56 kBit (modem).
Also, the reasons may lie in the large load of the EU server. It happens during public events, when there are many users on the server, and he does not cope. If you went to such a mass event (for example Oratan massacre), helps setting graphics in Low (less transmitted data) and disable Stream Audio. But sometimes in this mode there can be wrecks. Unfortunately, this problem can only be solved by EU developers.
For reference, add, that all ammo, that you planted in a fat Shared Loot mob, disappear, if you are offline at the time of the loot.