Connecting 4 18650 batteries in series without bms
It depends on chemistry. For example the Sony Konion doesn't need the BMS at all costs. It's a LiMn chemistry (IMR) also used in Samsung INR battery. Usually you will find those batteries in hand held tools battery packs, Makita does use Sony Konion with overvoltage and short circuit protection, no voltage measurement over each cell and BMS is done in their battery packs.
Simplified Makita Protection circuit:



simulate this circuit &ndash; Schematic created using CircuitLab
In case of overcurrent or short circuit the fuses F1 or F2 will blow. In case of overvoltage the comparator turns on the MOSFET which turns on the heating elements and starts to melt the fuse until the battery pack is disconnected from  charger, preventing the eplosion of the battery.
The protector fuse and heating element link