What's Thanos relevant feats.
1. Making blaster a bubble gun (matter manipulation)
2. Creating a pseudo scene to trick gamora (didn't actually change reality).
3. Killing half the universe with a snap
4. Using time gem to reverse gem from being destroyed.
From those feats we can only infer other things WITHIN REASON. NO WILD SPECULATION.
DM relevant feats
1. Can clone himself many times
2. Can see the future
3. Can become intangible
4. Can resurrect himself from total annihilation.
5. Can matter manipulate and remove intrinsic fields
6. Can perceive things on a Picosecond or less scale.
7. Can make himself resistant against harm (walking on the sun).
Questions that need to be addressed.
1. Can Thanos snap his fingers and kill DM permanently (DM can't resurrect)?
A. Will he think about that tactic and choose to do it within the first few moments of battle?
2. Will DM see the future and act accordingly?
3. Are we in control of both characters or will they operate (choose their tactics) in a manner typical of their film counterparts?
If 1. is a yes then Thanos can win if DM does not act first
If 1 is a no then DM wins
If 2 is a yes then DM wins
If 2 is a no then go to 1.
If 3 is a yes the DM wins.
If 3 is a no then go to 2.