I'm pretty sure DASH will do fine long term. It's a solid coin with a great devlopment team and roadmap. The problem with DASH mining is it's really a bad coin to mine with ASIC's. The mining subsidy adjusts lower as the difficulty increases, so it's a double wammy on your mining profitability. That creates a mining reward incentive if the difficulty drops too much and keeps large farms from centralizing the hash power and gaming the difficulty like happens with SHA256 coins. It also means as the network difficulty grows, there is also less new DASH to go around.
In a nutshell: the number of coins mined per block depends on the mining difficulty (which itself is based on global hash-rate for Dash) of the last block. Low difficulty means more coins per block, hight difficulty less coins. Additionally there's yearly decline of about 7% coins per block.
https://www.dash.org/forum/threads/total-dash-per-day-reward.14973/#post-127264Most people won't want to take a hit on the hardware they bought, so as long as it remains even slightly profitable they will keep mining. If it was me, I would say In for a penny, in for a pound and accumulate coins. That strategy worked out well for those that mined ETH and LTC with marginal to zero profitability for years until it finally turned around.