I know that this does not happen very often, but I was going against lluis83's Time/Aether in Top-50 with a Mindgate deck, and got very close to a tie. We both have Eternities and more shards for healing than the opponent's damage output. The only reason I ended up winning was because of the AI's stupidity.
This got me thinking:
What if two human players with Eternity went against each other, and both have enough regenerative power to completely recover from the opponent's damage immediately at end-game? The result would make the weapon of Time true to its name in the most literal sense... and the issue of who should forfeit would arise.
The most practical solutions I can think of:
Add the possibility of ending a match prematurely by consent. E.g. provide a 'tie game' button, upon the pressing of which a proposal to end the game would be presented to the opponent, with the options to accept or decline. If the proposal is accepted, the entry fee for the match would be returned to each player and no rewards would be given. The frequency at which the proposal button can be pressed could be limited to prevent abuse.
(on a related note, lluis83's Time/Aether vs. Mindgate actually does manage to avoid tied games due to the presence of the Anubis - whoever manages to immortalize all of the opponent's creatures first wins xD)
Edit:
Nevermind, the matchup does not always avoid tied games. All we need is one non-immortalized card for each player, heh.