crumbled, decayed, declined, degenerated, descended, deteriorated, devolved, ebbed, regressed, retrograded, rotted, sank(or sunk), worsened

abated, de-escalated, diminished, downsized, dwindled, receded, wanedbroke down, corrupted, decomposed, degraded, dilapidated, disintegrated, moldered, putrefiedsoured, spoiled(or chiefly British spoilt)lessened, lowered, reduceddebilitated, undermineddrooped, failed, fell, flagged, lagged, languished, ran down, sagged, slipped, wasted (away), weakened, wilted

went to pot, went to seed(or ran to seed)

ameliorated, improved, meliorated

bettered, upgradedenhanced, enriched, fortified, heightened, intensified, strengthenedadvanced, developed, marched, proceeded, progressed