It seems to me that you should at least keep Conquest. If you are the one and only civilization left on the planet then it is pointless to not declare yourself the winner. But all the victory conditions are optional - start a game via "Custom Game" and turn them all off. No modding necessary, as far as I know. I'm sure someone has tried a "no victory condition" game before, but not me.
I expect that eventually your civilization will start to decline, in some sense, as well. You've built every building in every city, researched every actual tech long ago and are now on future tech 142, and are stuck running every city in "produce gold" mode since the ever increasing inflation value now causes your maintenance costs to exceed the output from your 7 religious shrines (every city has had all 7 religions spread to it long ago). Then your sustainable percent research finally reaches 0 due to the inflation value. Before too much longer your income per turn will go negative. A few days of clicking on "end turn" after that you'll find it has disbanded all of your units, but it doesn't matter since there is nobody to fight. There is literally nothing to do in the game except click "end turn" since you have no units and nothing to build, except that every once in a long while a "you have completed Future Tech 257" type screen pops up for you to click on, and you might get some random event that has miraculously never been triggered in all those thousands of turns as well as those that can happen an unlimited number of times (your improvements have been wiped out around this peak for the 37th time due to the volcano type deal). So every once in a while you get to try to rebuild an improvement, or rebuild a building, that was wiped out by an unlimited random event. Eventually, they might wipe out all your improvements and buildings everywhere since you have no money to spend to prevent the effects from happening and your civilization is still on strike all of the time so you can't build any buildings anywhere and if disbanding workers can happen then you can't rebuild the improvements that get randomly wiped out either (which leads to starvation in your cities as all the improvements are wiped out and Sid's Sushi's food bonus goes to 0, except that I'm not sure if there is an event that wipes out seafood, ultimately leaving you with no happiness or heath or strategic resources, but that doesn't matter because of the huge amounts of happiness and heath you are getting from all your future techs and you can't build any units anyway so who needs strategic resources). And that isn't even taking global warming into account - that will eventually turn every land plot to desert. So here you are with dozens of empty cities on a bare map full of desert with no units still clicking away at "end turn" for hours on end, day after day, week after week, year after year. Sounds like a real exciting hobby. Or perhaps not.
Infinity makes for a bad game. Averaged over infinity, nothing ever happens. Anything that seems to happen is just a delusion brought on by the infinite amount of nothing ever happening.