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I think the wording of your question suggests that you may not understand the role of a UN peacekeeping force, or the rules under which military forces are required to operate in general.
In the video you linked, it states (at 9:00):
"The soldiers know that UN rules call for them to withdraw if their lives are in danger"
Those 'rules' are the Rules of Engagement (RoE) under which the entire UN force operates.
In general, the Rules for individual missions are not published by the UN in publicly available documents (for fairly obvious security reasons), although the Handbook on United Nations Multidimensional Peacekeeping Operations gives you some information about how their Rules of Engagement are prepared for each mission.
In the case of Bosnia, those rules have been published by other outlets, one example being Rules of engagement for U.N. peacekeeping forces in Bosnia by Bruce Berkowitz in the journal Orbis.
As @TomasBy observed in the comments, "Under international law, peacekeepers are non-combatants". One of the key issues is that for peacekeeping forces to operate, there must first be a peace to keep. (Otherwise, the mission becomes one of peace enforcement, requiring an entirely different set of RoE).
The Use of Force in UN Peace Operations by Dr Trevor Findlay provides some background on the history and conventions in force in this area. It also includes some examples of similar engagements that you might find of interest. However, of particular relevance here is the observation in the Introduction that use of force by UN peacekeeping forces:
"... is assumed to be limited to self-defence, as it may use force beyond this only with the consent of the parties. Since for the parties this would be tantamount to authorizing the use of force against themselves, such consent is unlikely to be granted."
Given that background, it is hardly reasonable to characterise peacekeepers who withdrew from an exposed position at a UN checkpoint, while under fire from an overwhelming enemy force, as - in your words - "ditching their posts" or "abandonments of their posts"! (Some idea of the force those peacekeepers were facing can be obtained from the Wikipedia article).
[NOTE: Contrast that situation with the recent (November 2018) case of the attack on a displaced persons camp in the Central African Republic, where it might more reasonably be argued that a UN force did abandon its post even before it came under fire]
The UN Principles and Guidelines for Peacekeeping operations has been substantially re-written since the 1990s (largely as a result of experiences in places like Rwanda and Bosnia).
In theory, this should mean that soldiers acting as UN peacekeepers should no longer have their hands tied when it comes to using force to defend the innocent.
In practice, that will depend very much on the quality of the troops being deployed.
To answer your specific questions: