I have the private keys to several outputs in the 0.01 — 0.1 BTC range. This kind of amount is quickly approaching dust level (https://bitcoinfees.earn.com/ currently recommends ~0.001 BTC for a standard transaction). Suppose I'm not at all in a hurry, what is the best strategy to avoid the outputs to become effectively unspendable in the future?

• Combine them all in a single output?
  
  • Since I'm not in a hurry, I could use a very small transaction fee, say one that gives the transaction a ~10 % chance of getting mined. If it doesn't get through, I can simply resend it.
  • I read somewhere that transactions stay in the mempool for 72 hours. Is that correct?
• Do nothing and just wait?
  
  • The lightning network should make sending bitcoins cheaper. But that per se doesn't help in this case as the small outputs are still there at a fundamental level.
  • However, if the lightning network reduces the number of actual bitcoin transactions, they should become cheaper.
  • The transaction costs may not go up much higher because only holders of larger assets would be willing to pay the fees, leading to an equilibrium.
• Something else?