and why should Russia have a "NEXT WAR" or "START A NEW WAR" with Ukraine in future? What are the objectives that Russia is trying to achieve in the "NEXT WAR" with Ukraine that it cannot simply achieve in the present war? This war has lasted since 2014 to present, almost 8 years (mostly via proxy), so Russia direct involvement should just end it now and achieve it's objectives, don't wait for a "NEXT WAR". This is the only war.
Well, it depends on what Russia's objective is.
If Russia's object is to stop Ukraine from joining NATO, then why should Russia NOT start another war with Ukraine if Ukraine started moving towards joining NATO in the future? If the current war will end with Russia and Ukraine sign a peace/seize-fire agreement which allow Russia to annex Donbass, Kherson Oblast, and majority of Zaporizhzhia Oblist (south of Zaporizhzhia city, the Russians control these land now). That creates a southern corridor for Russia to secure Crimea.
If Ukraine is willing to capitulate for a cease-fire/peace treaty, that's their reality: losing the 4 South-East provinces at least for sure. And that opens up a future war that could be started under a host of different pretexts.
Of course, this is all under the condition that the war is to stop now or very soon. I don't see Russia suffering a collapsing defeat in the south with any note worthy possibilities.