Not beatable. One would consider all stats at 99 a finished game, but no, oh no, that way Jagex can't empty your wallets, the game is finished when you rule the pking, have capped your gold, done all quests, and got all 99s
This is the game that never ends, it goes on and on my friends. Some people started playing it without knowing that it was, and blah blah blah blah blah i forget the final line.
Yeah the game is beatable depending on what your classification of finished is. I generally aim for a goal in MMORPG for me to consider a game beaten. For regular games I aim for 100% completion
It can be beaten. 200m all stats, every item obtained (mini game items, event items, etc.) The game just takes a very long time to "beat". I put that in quotes because in a sense you can only ever have the game beaten until the next update comes out.
It all depends on what you class as "beating" the game. I think getting 99 in all stats, and all quest points is winning the game. To others, it's quite different.
Technically, it would be possible, get the max amount of every item and cash, max out every skill, finish every quest/acheivement diary/unlock every song... Have all holiday items, emotes, ranked number 1 in every skill/minigame etc.
Everything, basically have everything.
You will have beaten RuneScape. (Until a new skill/minigame comes out)
Maxing out every skill and finishing all of the quest is 'beating' the game. Mastering the game would be getting 200k experience in all skills along with completing everything else the game has to offer. If you do ever 'beat' or 'master the game, wait one week and you will have to 'beat' and 'master' it again once another update comes out.