So the comment "Need for a God," I presume means something like is the most compelling explanation of the various data we have from our external world.
So this would be tantamount for, "What evidence do we have that there is a God or gods, etc.?"
"So if an infinite-regress were shown to be true then we would have no need for a God." I take this paraphrase of your OP statement to focus on causal arguments for God. So we might still have good reason to think God existed based on dozens of other arguments that do not intersect with ultimate causal arguments (teleological, moral, transcendent, arguments from mind, or even God's self-evident existence).
But let's ignore those for now and deal with infinite regress.
This is a huge question in philosophy. For a good survey of all the issues and positions see:
Infinite Regress Arguments (Stanford Encyclopedia of Philosophy)
So there are different arguments based on your underlying view of what one can know about the world and how.
"Metaphysicians have wanted to account for the very existence, or nature, of some things by appealing to things on which they ontologically depend: for example, a complex object exists and is the way it is because its parts exist and are the way they are; a set exists because its members exist; etc. (See Fine 1995 and Koslicki 2013 for discussion.) But of course the things the dependent beings depend on must themselves exist as well. Some have been suspicious of the idea that this can go on
ad infinitum, with every thing being ontologically dependent on some new thing(s), and thus have argued for Metaphysical Foundationalism: the view that there is a collection of absolutely fundamental[
4] entities upon which all else ultimately ontologically depends. Aquinas, e.g., holds that events are ontologically dependent on their causes, and that an infinite regress of causes and effects would be an infinite series of things each of which is ontologically dependent on the next, and this is impossible.[
5] Thus he concludes that there must be a first cause of all else that is itself uncaused—namely, God."
How Leibniz sorts out such matters is as follows:
"There cannot be only “beings by aggregation” (i.e., composite objects), because this would lead to an infinite regress, with each being by aggregation being made up of further beings by aggregation, and so on
ad infinitum.
Leibniz’s idea seems to be that if each thing depends on some other, there could not be anything at all in the first place. The thought is that ontologically dependent entities inherit their existence, or being, from that on which they depend; so if this chain of dependence does not terminate, the whole process couldn’t get off the ground, and there would be nothing at all. Leibniz says (1686–87, 85):
Where there are only beings by aggregation [composite objects], there are no real beings. For every being by aggregation presupposes beings endowed with real unity [simples], because every being derives its reality only from the reality of those beings of which it is composed, so that it will not have any reality at all if each being of which it is composed is itself a being by aggregation, a being for which we must still seek further grounds for its reality, grounds which can never be found in this way, if we must always continue to seek for them."
