"ㄹ테니까" makes a prediction with about 80% sure. like "will be~". Example sentence can be "I don't buy gold for a while, because gas price will be raised". "ㄹ텐데" is almost same meaning of "could", like the sentence "If I were a bird, I could fly." you can use "ㄹ텐데"when you imagine someone's feeling too. like "I saw someone punched, It must be really hurt". in this case, you never feel the someone's feeling. it is 100% impossible. so you can use the expression. add up. you can also use ㄹ텐데 when you suppose a situation which doesn't happen yet. like if mom comes in to my room, I would shout out to her get out..... well. "ㄹ텐데" is pretty complex. but one thing for sure is that means something that never happend yet. i think, it is close to the usasge of suppose. hope this makes to you. have a good day.

At the end of the sentence "ㄹ테니까" mean "(somebody) will (do something)" something is usually verb. For example, 누가 뭐래도 나는 날테니까. means "Whatever they said I'm going to fly." or it means guessing it will gonna happen. 그는 오늘도 운전할테니까. "He will drive anyway." When ㄹ텐데 is comes with end of the sentece it means same as "If I were ~". For example, 내가 새라면, 날 수 있을텐데. "If I were a bird, I could fly." Now when those are used in middle of sentence, ㄹ테니까 means "(sombody) will going to (do something)" For example, 나는 청소를 할테니(까)[you can skip 까], 너는 바닥을 쓸거라." "I'm going to clean up (something), then you are going to sweep the floor. ㄹ텐데 also has similar with previous usage even it used in the middle of it. For example, 그는 과자를 살텐데, 나는 무엇을 살까? "He's gonna buy some snacks, then what should I buy? When it goes middle, ㄹ텐데 is used as guessing (almost gonna do it). hope it helped :P