Yes he can save himself. Yes, he will lose his casting of Summon Monster V.

Summon Monster has a casting time of 1 round, and the spellcaster is required to concentrate on the spell for that duration (emphasis mine):

When you begin a spell that takes 1 round or longer to cast, you must continue the concentration from the current round to just before your turn in the next round (at least). If you lose concentration before the casting is complete, you lose the spell.

Duration states:

You can't cast a spell while concentrating on another one. Some spells last for a short time after you cease concentrating.

There is no exception for immediate action spells in there, nor anywhere else, meaning that you will have to drop concentration to cast another spell. The rules don't state any sort of action for dropping concentration voluntarily, but dropping it involuntarily (by failing a concentration check) is not-an-action, so I suggest doing with that.

They can use it, but if the random roll falls on a spell, it fails

The rule for casting multiple spells in one turn says:

You must use a bonus action on your turn to cast the spell, provided that you haven't already taken a bonus action this turn. You can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action.

So after casting a spell as a bonus action, there is nothing stopping you from using the wand as an action, but you cannot cast any spells above cantrip level on this turn.

Casting a spell from a wand is still casting a spell and plays by the same rules

While holding it, you can use an action to expend 1 of its charges and choose a target [...] Roll d100 and consult the following table to discover what happens.

If the effect causes you to cast a spell from the wand, the spell's save DC is 15.

The wand of wonder, like all wands, counts as you casting a spell. It is even in the description for the item. All the spell effects say:

You cast [Spell].

There is nothing that would excuse this casting from the rule that says:

You can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action.

And none of the spells contained withing the Wand of Wonder are cantrips.

Thus, if they used the wand after casting a bonus action spell and a spell effect is rolled, the spell would fail because it is not a cantrip.

Any of the non-spell effects would happen normally

There are no restrictions on the activation of other features of magic items though so it would not make any sense to disallow the use of the magic item entirely in this case.

If they cast a spell beforehand though, they will have to accept that there is a risk of them wasting their action with the Wand of Wonder.