Compared to the OT, which has a blueprint for individual and social ethics, NT ethics lack the same breath and detail. That doesn't mean OT ethics covers every conceivable situation, but it covers a lot more ground than NT ethics. Of course, that's because it was, in part, a civil and criminal law code for a nation-state.
However, the issue this raises is whether NT ethics is sufficient to give Christians moral and practical guidance on a host of issues where its silent.
Some Christians write off OT ethics in toto, as an inseparable part of an obsolete covenant. Some Christians focus on the Decalogue, but ignore the OT case law. Some Christians attempt to supplement NT ethics with natural law theory.
However, another move I've seen some Christians make is to appeal to what we might call sanctified intuition. Because Christians have the Holy Spirit, that gives us spiritual illumination in decision-making. So goes the claim.
Many of these Christians are technically cessationists, yet their appeal to spiritual impressions is wedge issue or halfway house between cessationism and charismatic theology. Instead of prophecy or an audible voice, they appeal to conscience as a tacit voice of God.
You also have Christians who are technically cessationists, yet they practice divination, although they don't call it that. They propose a situation to God. If something does or doesn't happen, depending on how they frame the test, they take that as a divine sign or answer to their question. That's another halfway house between cessationism and charismatic theology.
Ironically, it's Christians who combine a total rejection of OT ethics with hardline cessationism who end up resorting to divination, or acting as if their conscience is a divine oracle.