There are very few things clear about this at the moment actually. After several months of failed negotiations, deadlines, final deadlines, extended final deadlines and so on, OS supervisory board has decided to dissolve OS flight operations and merge them into VO flight operations by 1st of July this year - this much is certain.
Now, there is an Austrian law on such proceedings - the Arbeitsvertragsrechtsanpassungsgesetz (lovely German word, is it not?), which translates as Law on the adjustment of work contract legislation and is conveniently abbreviated as AVRAG. In short, it demands that the employees of the dissolved, merged corporation are not to have their T and Cs reduced and have to be treated as if they had been employees of the company taking over from the beginning. Consequently, OS staffs income will be frozen at current values until the figures according to VO contract have caught up in some years and only then be raised. Also, the seniority lists will be joined according to the dates of entry into the respective employees initial contract. For VO original staff, the T and C remains intact.
But there is a large source of uncertainty that will likely allow many lawyers to have a field day. In February, management has cancelled the OS collective labour contract (CLC from now) unilaterally due to unsatisfactory progress in the negotiations, which the union responded to by cancelling the VO CLC as well (one might add that no-one at VO has approved of this or was even consulted beforehand; many see this as high treason by the union). Austrian law states that a cancelled CLC continues to remain in effect for those governed by it at the time of its cancellation until a new agreement is made. So OS staff is now forced to enter a CLC-less space; management has already announced that every previous OS employee will be offered an individual contract with T and Cs probably even below VO standard. Seems like the union has cut its own throat by their actions... But back to the AVRAG, which also states that every employee of the dissolved corporation has a special resignation right that will trigger compensation payments from the employer; sums of up to 39 monthly salaries are expected. And here is where the legal views differ massively. According to the union, these payments are due when the T and Cs applicable after the takeover are much worse than the old ones; management however has taken the point of view that it is not the T and Cs, but the CLC that matters - and as there is no more CLC applicable to the former OS staff, no payments are expected. A field day for lawyers coming up.
So to answer Your questions in a nutshell:
-Yes, the former Austrian staff will join Tyrolean ranks.
-Yes, this is independent of what fleet they are on.
-Yes, wage growth is stopping; but not more than this - there will be no reduction either.
-No, Tyrolean T and Cs are intact and neither present pay nor other schemes are to be reduced.
A strike is possibly in the woods, but only on the OS side of the fence - some actions of OS like the cancellation of the VO CLC have been highly efficient in quenching the solidarity VO staff may have felt before.
Some former OS staff may indeed decide to call it quits and head to the sandbox; figures quoted are ranging from 50 to several 100.