There is no wisdom for the un-united, nor concentration for the un-united; for one who does not concentrate there is no peace, and for one deprived of peace, whence happiness?

The chain of deprivation: ayuktaḥ (un-united, not in yoga) lacks buddhi (discernment), then na bhāvanā (there is no concentration/mental tuning).

Without bhāvanā, na śāntiḥ (there is no peace). Without śānti, kutaḥ sukham (whence happiness?). The question is rhetorical: happiness without peace is impossible.

The structure is regressive: lack of yoga → lack of wisdom → lack of concentration → lack of peace → impossibility of happiness. Yoga is the condition of all realization.