I was once in a position like yours with a couple of properties. I saw it coming and sold as fast as I could. The places were still worth money and full occupied...but I could see where the neighborhood was going to be in a couple more years....get out while there was still something worthwhile to sell.
When the first drug bust in the neighborhood happen, I knew where that was heading. I put the places on the market then next day. That was back in 2005. I knew that once I could only get sect 8 renters I would never get rid of the properties. I lost money on the sale...but..It wasn't anything as bad as you describe. (btw..there was a drug related shooting in the house right next door the day after I closed the sale).
So.. I wouldn't tell the tenants anything. Given your situation, I would not bother trying to collect rent either...then they won't start other complaints to the city about lack of maintenance.