Recently, we have learned that SDL sold Fredhopper. It means SDL will discontinue the SmartTarget product?
No, even though Fredhopper is sold by SDL, SDL SmartTarget continues to rely on Fredhopper as the indexing/querying engine, no matter the owner. To be more precise, this is true for 2013, Web 8, Web 8.5. With Tridion Sites 9, there will be a different indexing/querying engine in use. But that does not affect Smarttarget, or rather Experience Optimization (XO) as it's called starting from Web 8 onward.