The 146/RJ can not dump fuel. If you want to reduce landing weight or fuel you have to burn it off.
Rather than looking at distance travelled, look at time airborne. On average the AC will burn 2000kgs per hour, taking into account take off, climb, cruise and descent. The AC took off at 2218z and disappeared at 0255z. That's a flight time of 4:37hrs and roughly 9000kgs of fuel burnt. The max useable fuel quantity is 9300kgs. Unless pannier tanks were added (I personally don't think this is a financially viable option for a South American operator buying a relatively cheap regional jet). This would increase useable fuel to 10300. The AC definitely declared an electrical emergency. Then continued to hold PRESUMEABLY to deal with the checklist etc. To have a electrical failure due to lack of fuel is an idiotic assumption as the immediate emergency would be the flameout of engine/s.