There's a lot of variables in play...
- To what extent the Taiping have moderated their views.
- Obviously, the more moderate they are the less likely they are to alienate their new subjects.
- If they're still going on about land reform the gentry will be uneasy, and if they're going around smashing traditional temples they'll earn the enmity of the peasants.
- How the western powers feel about things and what Taiping/Western relations look like.
- E.g. Taiping policies on opium, how they treat western envoys and missionaries etc.
- When the Taiping have defeated the Qing-
- The later it is, the more China has been trashed by war (with all the attendant economic and social effects).
- Relations with the west could be effected by whether this is before or after the Second Opium War.
- If Yang Xiuqing is still around that probably isn't great for the stability of the Taiping regime.
- How the other rebellions are going (Nian, Panthay, Dungan, Miao) and how they interact with the new Taiping regime.
- Whether there's still members of the Qing dynasty floating around to cause trouble.
Honestly, I'm not sure the Taiping have the manpower and organisational capacity to properly assert control over all of China, at least in the short term.
Their support also isn't very broad-based, and their best bet is watering down their extreme views and presenting themselves as just another change of dynasty (i.e. Talk about the Mandate of Heaven and getting rid of the Manchu, rather than all the religious stuff). Whether Hong "God's my Daddy" Xiuquan would be at all amenable to this change of direction is another matter entirely, and I'd have severe doubts about the stability of any regime with the likes of Xiuquan at its head.