Seedling with shrunk and darky true leaves

No, if it loses it first true leaves, that's it, no new ones will ever grow. Their "disappearance" was likely due to too high a humidity, especially if you had covered the newly hatched seedling with cling film or other humidity boosting cover. Cannabis seedlings do not need artificially high humidity to grow, but they do need good air exchange, something that can not happen when under a cover of any sort. Having a light on can also raise the temperature under the cover considerably, literally cooking any new growth or causing moulds or fungus to attack the plant. Cannabis is not a rain forest plant and growing seedlings under humidity domes/sweat lodges is one of the most frequent mistakes I see in Grow Diaries. Only cuttings/clones need extra humidity, and only for a short time while they are waiting to form a new root system. Just think about what happens in nature, cannabis grows in the open air, there are no little elves or fairies running around covering cannabis seedlings with little humidity domes or plastic film. Most Idicas come from the middle east, a very dry climate and most sativas come from equatorial countries and grow in the "dry" season, both environments are very low in humidity. Cannabis needing humidity is an outdated concept from the 1960s when pot was coming from South East Asia (and people generally had very little actual knowledge about cannabis), so people though "jungle", whereas the pot came from low land areas and grown during the dry season. This myth about cannabis needing humidity has strangely persisted for the last 60 odd years and is largely an urban myth. I also believe people are wasting vast amounts of money by unnecessarily having and running humidifiers in their grow tents/spaces. Cannabis actually prefers a dry environment from mid flowering onwards, and will produce the largest amounts of trichomes when its is arid at the end stages of flowering. Hope this helps, Organoman.