IMO, the merger will happen eventually. Whatever concerns have been raised in opposition to merger hopefully can be resolved with written assurances/commitments from T-Mobile.
... plus taxes, so really more like $30. I, personally, would strongly consider T-Mobile then as while both are good around town, Sprint signal is bad at my house (T-Mobile is excellent).
A T-Mobile-Sprint merger is a threat to MVNOs, as Sprint is the biggest wholesaler for MVNOs and a merger company will likely no longer offer aggressive wholesale pricing.
Sprint is losing money, so if without the merger, it will simply disappear in a few years... so not much different outcome. The big difference would be who gets Band 41. With merger, it will be T-Mo. Without merger, it could go to any of the remaining Big 3.