the mentality (or how to RP) a Manei Domini. While they are from the Inner Sphere culture, the MD are absolutely fanatic... To me they would not have the same sense of self-preservation other IS troops exhibit, best expressed about 'living to fight another day.
In my mind it really depends on the soldier. The way I play them out is as follows (this is only my opinion, and probably not canon):
WoB Militia: These guys are for the Word, but are not overly fanatical about it. They won't take highly unnecessary risks to win a fight, are willing to surrender if they see it is for the best or if it is a losing fight, but probably wouldn't talk to much during interrogations. In the end, many of them are rank-and-file ex-Comstar employees, or planetary militias that the Word gave equipment and training to.
WoB Manei Domini, rank and file: These guys are super fanatical. They are the ones that call in artie or air support danger close because screw the enemy. They use anything at their disposal to win a fight, and would rather die than surrender; usually they do die while they surrender as they blow up a suicide vest in the hopes of killing their captors.
WoB Opacus: Fanatical, but not as much as the Venatori. Probably a bit more sense of self preservation since they are the elite of the elite, and would rather abandon a mission than be taken captive, but were not willing to get implants to replace body parts. Most of this group can probably hide within public fairly easily since they don't have any significant implants, or none at all for most of them, so they could abandon their equipment and disappear.
WoB Venatori (excluding Berith): Super fanatical. Again, willing to use any means at their disposal to win a fight. I think these guys are a bit more willing to die fighting than the Opacus or the Militia, however it depends on the situation. If they are hunting a high value target perhaps retreat and fight another day. If it is defending something highly critical to the success of the Word, then defend or die.
Berith: I don't see him as willing to die for the cause unless it is specifically ordered by the Master. In my mind, because of his station and status within the Word of Blake, I would say this dude is going to live to fight another day. Otherwise, similar types of tactics as the other fanatics; WMDs, oribital bombardments, whatever is at his and his teams disposal to win will be used. This dude is willing to kill anyone, including his allies, if it is commanded by the Master.
Again, just my thoughts on how to RP them during combat. I have never played the RPG, so I don't know how I would RP them in non-combat scenarios.